1. Field of the Invention
The present invention relates to equal-sized abrasive agglomerate beads coated on both abrasive raised island and planar media, and also, to processes for manufacturing both the abrasive beads and raised island articles. The media are thin flexible abrasive sheeting used for grinding or lapping, workpiece surfaces. In particular, the present invention relates to media having the equal-sized abrasive beads or agglomerates bonded in monolayers to the flat surfaces of backing sheets. The sheets can also have raised island shapes that are repeated in patterned arrays where the top flat surfaces of the islands are coated with monolayers of the abrasive beads. The abrasive sheets and the raised island sheets can have a disk shape with an annular distribution of abrasive or the sheets can have rectangular shapes. The abrasive sheets can move against a stationary workpiece or the abrasive can be held stationary and a workpiece moved while in pressure contact with the sheets. Planar (non raised island) abrasive articles can be coated with the equal sized abrasive beads by many continuous web or sheet coating techniques that are in common use in the industry. The raised island abrasive articles can be manufactured with abrasive raised island surfaces, where the island surfaces are located in a common plane that is precisely parallel to the back mounting surface of the backing sheet. The individual island structures have thin top coatings of abrasive particles or abrasive agglomerate beads that are adhesively bonded to the top flat surfaces of the island structures, preferably in single or monolayers of particles or beads. The raised island abrasive articles can be used at high and slow abrading surface speeds where all or most of the abrasive particles are utilized in grinding or lapping flat workpiece surfaces. Small abrasive particles or abrasive bead agglomerates must be in direct contact with a workpiece to enable them to create material removal from the workpiece. Coolant water is typically used with abrasive grinding or lapping of workpieces, particularly for high speed abrading operations. The water cools workpiece surfaces and also cools the abrasive material where both are mutually heated by the friction heating of the abrasive moving in pressure contact with a workpiece. Overheating of abrasive particles can destroy the cutting capability of the abrasive. Coolant water can freely pass through the recessed flow channels formed as valley passageways between the raised islands to flush out grinding swarf and to exhaust excess water. This prevents swarf debris particles from scratching the surface of a workpiece when they can be lodged between the moving abrasive and the workpiece surface.
The formation of a boundary layer of coolant water on the surface of a workpiece or the hydroplaning of a workpiece on the surface of the abrasive can have a large effect on abrading the workpiece. If a portion of the workpiece is floated too far above the abrasive due to the separation caused by the thickness of the induced water boundary layer, no abrading contact is made with the workpiece in the area that has undersized beads or even full-sized beads in some cases. Because of this, it is desired to have equal-sized abrasive beads where all of the beads can be in contact with a workpiece. Hydroplaning of the workpiece when abrading at high surface speeds is minimized as a large proportion of the abrasive coolant water can pass between the raised island structures. Thick boundary layers of water that are usually formed between workpiece flat surfaces and flat-surfaced abrasive articles at high abrading speeds are diminished in thickness when an island-type abrasive is used. The water boundary layer thickness grows in magnitude as a function of the continuous water contact length between a workpiece and an abrasive surface. The water contact length is measured in the vector direction of the relative abrading speed between the workpiece and the abrasive. The reduced abrading-surface contact lengths of individual abrasive islands present shorter water contact lengths between a workpiece and an abrasive surface than occurs for a comparable continuous surface abrasive article. The short water-contact lengths of the island surfaces can produce substantially reduced water boundary layer thicknesses if the island surface length of the island is sufficiently short in the direction of relative motion between the abrading surfaces. Islands may have long lengths in a direction perpendicular to the direction of movement as the water boundary layer builds up in thickness from a leading edge of contact to the trailing edge of contact in the vector direction of the abrading relative surface velocity. Water boundary layer thickness is a function of a number of process variables including the abrading vector velocity, the viscosity of the water lubricant, the distance from the leading contact edge, the surface roughness and surface flatness of both the workpiece and the abrasive media and the contact pressure between workpiece and the abrasive article. However, in most abrading applications, the type of abrasive article, the abrasive particle or abrasive agglomerate size, the abrading surface speed, the contact pressure and the water lubricant are set or optimized for a given workpiece. The one important variable than can be changed is the use of an island type abrasive article in place of a continuous abrasive surface article to reduce the boundary layer thickness and to provide a free passage of grinding debris away from the workpiece abrading contact area. In the case of lapping, water traveling down the passageways that exist between island structures can flush abrasive media or workpiece debris particles out of the abrading contact areas and reduce the possibility of workpiece scratches. The same highly desired monolayers of abrasive bead agglomerates, each containing small sized abrasive particles, can be used on the island top surfaces as that which are presently used on abrasive articles having continuous flat abrasive surfaces. Island type abrasive is known to produce flatter workpiece surfaces than does continuous surfaced abrasive sheet article, particularly when used at high abrading surface speeds. Improved workpiece flatness when abraded with island abrasive is discussed in patent literature. High abrading speeds are desired for achieving high workpiece material removal rates by diamond and other abrasive materials. If the water boundary layer thickness varies over the surface of the portion of the workpiece being abraded, then the abrading contact between the workpiece and the abrasive media can vary and non-flat workpiece surfaces can be generated. It is desired to have uniform contact between the workpiece and the abrasive media over the whole abrasive contacting surface of the workpiece to generate flat surfaces. It is also preferred that the abrasive beads have a diameter size that is from 30 to 60 micrometers and that the standard deviation in size of the beads is less than 50% of the bead size to create an abrasive article that is precisely flat and that utilizes all of the abrasive particles that are contained in each abrasive agglomerate bead. The precision thickness control of the backing sheet abrasive articles assures that all of the abrasive material coated on an abrasive article contacts and abrades a flat workpiece. However, it is also necessary that the flat surface of the platen to which the abrasive sheet article is attached is also precisely flat so that the exposed abrasive surface is in flat contact with the workpiece surface. Lapping workpieces require both flat abrasive sheeting articles and flat abrasive article mounting surfaces even at low abrading surface speeds. At high abrading surface speeds, raised abrasive coated islands can prevent the formation of large boundary layers of coolant water between the workpiece and abrasive surfaces, which in turn, can prevent the creation of precisely flat workpiece surfaces.
2. Background of the Invention
Island type abrasive articles have been produced for many years, particularly for abrasive disks used on manually operated hand grinders. The islands have a variety of shapes including annular bands of discrete island shapes and generally had a repetitive geometric pattern. Many of the earliest abrasive islands were patterns of individual areas of abrasive that were flat coated on a backing sheet or backing disk with non-abrasive coated gap spaces located between the island shapes. Some early abrasive islands were raised island shapes that were produced by a variety of methods. In one of the earliest methods a very thick layer of make coat adhesive is applied to a backing disk, abrasive particles are then deposited on the surface of the thick adhesive and then embossing dies are used to push down portions of the abrasive coated adhesive which raised other adjacent portions to form abrasive coated raised island structures. This technique only was possible with thick coated sub layers of adhesive as it would not be possible to form the raised islands with a thin layer of adhesive with the embossing dies. In another of these same very early methods, individual raised island structures were independently formed in patterns on a backing sheet and these raised structures were then coated with a layer of abrasive particles that were adhesively bonded to the island structures. More recently, raised island structures are been formed on a backing sheet and the top surfaces (only) of the island structures are coated with abrasive particles or tooth-formed shapes of an abrasive layer. None of the referenced prior art abrasive coated raised island structure patents, other than Duescher in U.S. Pat. Nos. 6,752,700 and 6,769,969, address or teach the desirability of having layers of abrasive particles or abrasive agglomerates coated on precise height island structures to produce an abrasive article that has a final product precise thickness measured from the top surface of the abrasive media to the bottom surface of the backing sheet. Also, these other prior art patents do not teach of the desirability of using mono layers of abrasive particles or agglomerates on the top surface of the island structures.
An abrasive product from 3M Company is the pyramid shaped Trizact® abrasive, which helps with hydroplaning effects when used for high abrading speed processes. Coolant water flows between the tops of the pyramids when the abrasive article is only slightly worn and there are significant recessed water passageway channels between the pyramid tops. These recessed channels are substantially reduced as the Trizact® article becomes worn down and hydroplaning can become more significant. After the pyramid tips are worn down and the pyramid shape is reduced in height, the abrasive article tends to behave more like a more conventional abrasive article that has a continuous coating of abrasive as the coolant water passageways that lie between the tips are reduced in size. Also, it is only practical for this shaped pyramid product to be created with inexpensive abrasive media such as aluminum oxide as most of the volume of abrasive particles reside in the base of the pyramids and are only in abrading contact with a workpiece when the abrasive article is substantially worn down. Use of expensive diamond particles in these pyramid structures is not practical as much of the volume of the diamond particles that reside in a pyramid may not be utilized, particularly when the abrasive article is mounted on a platen, or other, mounting surface that is not precisely flat. Abrasive articles having patterns of shaped pyramid abrasive structures attached to a backing surface tend to wear fast and unevenly across its surface. These are a continuous web type of abrasive article products that typically do not have the precise article thickness control required for high speed precision flat lapping.
Coated abrasives typically have a plurality of abrasive particles or abrasive agglomerates bonded to a backing by means of one or more binders. Coated abrasives utilized in polishing processes are typically in the form of endless belts, tapes, or rolls that are provided in the form of a cassette. Examples of commercially available polishing products include “IMPERIAL” Microfinishing Film (hereinafter IMFF) and “IMPERIAL” Diamond Lapping Film (hereinafter IDLF), both of which are commercially available from Minnesota Mining and Manufacturing Company (3M Company), St. Paul, Minn.
High speed lapping can be accomplished with the use of thin flexible abrasive coated disks or sheets that are very precise in thickness and that are attached to a platen that is very flat and stable. When a platen having an attached abrasive disk rotates very fast, the high speed contact of the abrasive with the workpiece tends to “level” the abrasive surface as it is presented to the workpiece surface. As only the high spots of the abrasive contact the workpiece, the remainder of the disk abrasive is not used until the high spots wear down. Thus, it is necessary for the total lapping system equipment to be precisely aligned and constructed of precision components to provide precision abrading action, particularly at the start of the process when a new abrasive article sheet is first attached for use. Furthermore, the wear of the abrasive must proceed uniformly across both the surface of the planar abrasive sheet and across the surface of each island to maintain the required flatness of both the effective abrasive surface and correspondingly, the workpiece surface. Various configurations of high speed lapper machines along with different abrading process techniques employed in operating the machines have been defined. Lapping equipment and lapping process procedures that apply are taught by Duescher in U.S. Pat. Nos. 6,149,506, 6,120,352; 6,102,777; 6,048,254; 5,993,298; 5,967,882, 5,910,041, 6,752,700 and 6,769,969 which are incorporated herein by reference.
The manufacture of flat surfaced raised island abrasive articles that are to be used in lapping or flat-lapping is critical in that the finished article product should have abrasive particles that are all bonded to an abrasive disk article at the same elevation from the backside of the abrasive article. It is not critical to control the absolute height of abrasive flat islands as the depth of the water passage valleys located between the island structures can vary considerably and still perform the function of a simple water passageway. The total thickness of the monolayer abrasive coated abrasive article must be controlled to within a small fraction of the size of the abrasive particles or agglomerates coated on the island surfaces. This thickness control can be accomplished quite easily by using abrasive media production equipment that has approximately the same precision flatness and motion accuracy as the lapping machine equipment that is required to effectively use the abrasive article for precision-surface high speed lapping. Traditional methods of producing lapping disk articles is to abrasive coat a continuous web sheet and die-cut or punch out disks or sheets from the web sheet. Producing a precision flat workpiece surface when abrading with a non-flat abrasive disk article is difficult. Rectangular arrays of raised abrasive islands or flat surface abrasive coated backings can also be used for a variety of abrasive articles including: rectangular flexible flat abrasive article sheets where a workpiece can be moved relative to the abrasive sheet; continuous abrasive strips or abrading-tape articles; and also, endless abrasive belt articles. A slurry mixture of abrasive particles or composite abrasive agglomerate beads mixed with a solvent diluted resin can also be applied to bare or primer coated island tops or directly on the surface of backing material. Here, the top surface of individual abrasive beads are exposed from the surrounding surface of the abrasive bead supporting resin that is used to bond beads to the island structure top surfaces or backing sheet, after evaporation of the solvent. Batch manufacturing of small groups of individual annular band abrasive articles allows the utilization of quick response manufacturing techniques for specialty abrading applications. The batch process production rates can be increased substantially with a hybrid enhancement of producing resin transfer coating sheets that are used to transfer coat a abrasive resin slurry or a resin make coat to a backing sheet. A simple hand-spread notch-bar coater can be used to apply a resin make-coat or a abrasive slurry coating onto a continuous web backing material that is then cut or converted into transfer rectangular sheet or circular disk segments. Individual backing sheets having attached raised islands or non-island backing sheets can then be placed in flat contact with the resin or slurry coated transfer sheet web-sections that have been cut-out from the coated web. When the transfer sheet is separated from the backing, approximately 50% of the transfer sheet resin or slurry thickness is transferred to the surface of the target raised island or non-island backing sheet. In the case where a make coat of resin is applied to a backing material, abrasive beads are applied to the wet resin to form an abrasive coated backing.
Lapping and grinding can be performed on the surface of a workpiece part by placing the workpiece in moving contact with an abrasive sheet and controlling the contact force holding the workpiece against the abrasive. To create this abrading action either the workpiece can be moved along the surface of the abrasive or the abrasive can be moved along the surface of the workpiece. An increased contact force results in higher workpiece material removal rates and a more coarse or rough workpiece surface finish. A reduced force results in a smoother finish but lower material removal rates. Water, which is often used both as a coolant and also as an agent to flush grinding swarf from the contact area between the workpiece and the abrasive can cause hydroplaning of the workpiece when there is a high relative surface speed between the workpiece and the abrasive article surface. A continuous film of water present at the moving contact interface surface area between the workpiece and the abrasive surface tends to separate the workpiece surface from the abrasive surface. Hydroplaning of the workpiece occurring during the abrading action tends to develop cone or saddle shapes on the workpiece surface thereby preventing the formation of a precision flat workpiece surface. Use of raised abrasive top-coated flat surfaced islands attached to a backing sheet allows passage of water within the passageways formed by the valleys between islands while the abrasive is maintained in direct contact with a workpiece surface. Each abrading island contact raised land area is flat across its surface and can be used for flat lapping or flat grinding of workpiece articles.
In flat lapping or polishing where a flat workpiece surface is presented in surface contact with a flat abrasive article to produce cutting, grinding or polishing action where the contact surface pressure, in pounds per square inch or newtons per square cm, is uniform across a portion of, or the full surface of the workpiece. Contact pressures are typically controlled to be low at the onset of the polishing process, increased progressively and then decreased in the final phase of a lapping operation to obtain the most effective utilization of the abrasive media. A single or mono layer of abrasive particles or agglomerates is highly desired for flat lapping of workpieces including pump seals, bearing seals, optical components including but not limited to a lens, a fiber optic connector, optical crystals, and semiconductor substrates. Abrasion may take place where the workpiece is held stationary and the abrasive sheet article or lapping film is moved relative to the workpiece. Lapping film is a abrasive article having a thin, flexible polymer backing coated with abrasive particles or coated with spherical bead abrasive agglomerates. Also, abrasion may occur where the abrasive article or lapping film is held stationary and the workpiece is moved relative to the abrasive article. Relative surface speeds of the abrasive may be considerably less when moving the workpiece relative to the abrasive sheet than the abrasive speeds that are used in high speed lapping. In high speed lapping, the moving abrasive sheet typically has very high surface speeds to take advantage of the high cut rates that occur when using diamond abrasive at high surface speeds. Abrasive lapping sheets, commonly referred to as lapping films, typically have very precision thickness abrasive sheet article thicknesses and also have monolayer thickness abrasive particle coatings that are critical to produce the very precise flat surfaces and the very smooth polished surfaces required for optical workpieces and fiber optic devices.
Abrasive lapping of workpieces requires that fixed-abrasive sheet articles produce both a flat surface and a smooth surface. Polishing of a workpiece only requires a production of a smooth surface. Use of fixed-abrasive sheet articles has many advantages over the use of a liquid abrasive loose-particle slurry mixture. High speed lapping with a fixed-abrasive sheet takes advantage of the very high material removal rate of diamond abrasive that occurs when it moves at a high surface speed against the surface of a hard workpiece. Slurry lapping requires a slow abrading surface speed because of the limitations in shearing the liquid slurry mixture as a workpieces is held against a flat platen coated with the abrasive slurry. A preferred form of fixed-abrasive used for lapping is very small abrasive particles having sizes from 0.1 to 3.0 microns that are encapsulated into porous ceramic beads that have a modest sized diameter of 45 microns. These beads are bonded to the top surface of a thin backing sheet having a precise thickness to form a abrasive sheet article. The small abrasive particles provide a smooth workpiece finish and the larger beads provide sufficient abrasive material for a long life of the abrasive article. The 45 micron beads are not too large to create significant low-spot abrasive areas on the article during the abrasive wear down of the beads that occurs during abrading. These low-spots can result in non-flat workpiece surfaces. Almost all of the abrasive particle material contained within the individual spherical abrasive beads is contained at the center of the bead sphere which is located at 22.5 microns (one half the sphere diameter) up from the backing sheet top surface. Therefore, most of the workpiece material removal is provided by abrasive particles that are located at a narrow range of height variation from the top surface of the backing sheet which acts as a natural process mechanism to provide flat workpiece surfaces. When all of the beads are of an equal diameter size then all individual beads contribute equally to material removal. Beads can be coated directly on the flat surface of a backing sheet or the beads can be coated on the top flat surfaces of raised islands that are attached to backing sheets. Abrasive articles having a single or mono layer of individual abrasive particles or composite abrasive agglomerate beads coated on the flat surfaces of a flexible backing media provides the capability to grind and polish workpieces both flat and smooth during lapping and grinding operations. To have accurate and smooth high speed lapping it is critical that the abrasive be worn evenly across the abrasive article surface to maintain the presentation of a flat abrasive surface to workpiece surfaces throughout the working life of the abrasive article. It is also very important that all the abrasive attached to the surface of an abrasive article be positioned at the same elevation relative to the backside of the backing to allow contact of all of the individual particles. High abrading surface speeds are desired to effectively utilize the cutting action of diamond abrasive that can produce very high material removal rates on very hard substrate workpiece materials. However, diamond abrasive is also often used for low speed grinding or lapping, particularly when a workpiece is moved relative to a fixed position or slow moving abrasive sheet. Individual large abrasive particles can also be coated directly on the surface of a disk backing and used effectively for grinding. However, the small abrasive particles that are required to produce precisely smooth workpiece surfaces are too small to be directly coated on backings. Instead, small abrasive particles are joined together in agglomerates or beads having a larger size and these larger sized beads are coated with space gaps between individual beads on a backing sheet to form an abrasive article. A method is described for forming equal-sized composite spherical glass or ceramic beads with the use of a open mesh screen material. The beads can be solid or hollow. The beads may be comprised of a ceramic material or the beads may be comprised of a agglomerate mixture of different materials including ceramic materials and abrasive particles. Abrasive particles of different sizes may be incorporated into individual beads. Different types of abrasives including diamond, cubic boron nitride, aluminum oxide and other abrasive particles, and also non-abrasive materials including metals and lubricants or combinations thereof can be mixed together within the individual beads. Hollow abrasive beads may be formed where the ceramic and abrasive mixture forms the shell of a hollow abrasive bead. Preferably, the beads are abrasive agglomerates comprised of very small abrasive particles enclosed by an erodible ceramic matrix material.
Use of monolayers (single layers) of abrasive particles or abrasive composite agglomerates maximizes the use of individual abrasive particles and allows flat grinding of composite dissimilar workpiece materials including semiconductor devices having metal embedded within ceramic materials. Abrasive monolayers coated on backing sheets or coated on the top surfaces of raised island structures prevent the second-tier level of individual abrasive particles that are bonded at a raised elevation to particles bonded directly to a backing surface from digging out soft material workpiece features from hard workpiece substrate materials. Soft material “pick-out” can occur when the elevated non-monolayer abrasive particles are forced down into the workpiece embedded soft material by the abrading contact forces becoming concentrated upon the single raised particles as the abrasive moves relative to the workpiece surface.
When an abrasive article used for polishing that has a mono or single layer of abrasive particle or agglomerate or bead coated media, there will be less pick-out of softer materials, or discrete hard foreign nodules, located in pockets on the surface of hard workpiece articles than there will be when abrasive articles having stacked particles on the coated abrasive media. Workpieces having these characteristics that are susceptible to pick-out include semiconductor devices having soft metal conductor material imbedded in trenches in hard ceramics material and cast cylindrical automotive parts having carbon or other precipitated inclusions on the part surface.
Spherical bead composite agglomerate abrasive particle shapes are a preferred agglomerate shape for creating a single layer or monolayer of composite agglomerates on a backing sheet. The spherical shape provides more consistency in shape and consistency in slurry coating or abrasive particle drop coating than do acicular shaped or irregular shaped agglomerates formed by crushing a hardened abrasive composite material. The geometry difference between an agglomerate sphere shape and an agglomerate block shape has a pronounced effect on the utilization of individual abrasive particles coated on an abrasive article. The primary bulk of individual abrasive particles contained in a spherical erodible abrasive composite agglomerate are located at the sphere center of the spherical agglomerate which is positioned a sphere radius distance above the surface of a backing sheet. When the agglomerate abrasive spheres are raised to an elevated position above the backing surface, the elevated position of the bulk of the sphere-contained individual abrasive particles assures that most of the particles contained in a spherical agglomerate are effectively used in abrading action as the abrasive article becomes worn down. An abrasive article is usually abandoned prior to wearing all of the agglomerates completely down to the agglomerate base that is adhesively bonded to a backing surface that gives an abrasive particle utilization advantage to spherical agglomerates over block shape agglomerates. Few of the original total quantity of unused individual abrasive particles are contained in the remaining truncated hemisphere small-volume areas of spherical agglomerates that are left attached to a worn-down abrasive article backing-sheet. Comparatively, a larger portion of unused individual abrasive particles reside in the remaining truncated block-shape non-spherical agglomerates worn-down to the same height level above the backing surface as for the worn-down spherical agglomerates. The number of abrasive particles contained in the highly reduced volume in the inverted apex of a diminished truncated sphere are very small compared to the particles contained in the linearly reduced volume agglomerate block shape bonded flat to a backing sheet. Some coated abrasive particles including individual abrasive particles, abrasive agglomerates and spherical abrasive beads are often stacked at different levels where some of the particles are positioned 50% of their diameters above the height of like-sized particles which are located in direct contact with the surface of the backing sheet. Other particles are often stacked in layers that are positioned two or more particle diameters above the backing surface. These “high-positioned” particles are few in number compared to those positioned directly on the backing surface but these high-risers have an exaggerated effect on polishing a workpiece. Although not wanting to be bound by theory, it is believed that the high positioned particles will tend to reach down into the soft portions of a hard substrate surface and gouge out or selectively abrade away the softer material as the abrasive travels in abrading contact with the substrate surface. In the case of the force tensioned abrasive tape system, the abrading contact pressure that acts normal or perpendicular to the substrate or cylindrical journal surface is quite low compared to the normal surface contact pressure present in the nip-roll abrasive system. Less pick-out of soft materials will occur with the abrasive tensioned tape system than with the nipped roll abrasive belt system. The nipped belt having the relatively high contact pressures in the central land area will aggressively loosen and dispel the hard foreign surface particles or erode and gouge out soft material areas whenever a raised surface abrasive particle comes in contact with the foreign material nodule or the soft material. All of the localized high nip roll contact pressure tends to become focused on the high level abrasive particles which drives these individual high particles down into the soft material whereas the bulk of the same sized adjacent particles are self-bridged across the soft area and are principally in contact with the hard substrate parent material surface. These high particles or agglomerates also can tend to apply large impact forces to imbedded foreign surface particles when the abrasive is moving at high speeds in contact with the workpiece surface and dislodge the imbedded particle, leaving a crater in the surface of the substrate or cylindrical metal surface. Dislodging foreign particles can occur in the process of high speed lapping; where surface speeds of 10,000 surface feet per minute or more can be reached.
A wide range of diamond or other abrasive particles or abrasive agglomerates or spherical abrasive beads are commonly attached to the surface of abrasive articles. Some abrasive particles are faceted crystals having sharp edges on many sides. The sharp particle edges provide cutting surfaces that are brought in pressure contact with a workpiece to cut, grind or polish the workpiece surface. Ceramic bead composite agglomerates for a particular classification of diamond particles also tend to have different spherical diameters for a given particle size classification. For example, a 3-micron diamond particle classification abrasive article may be supplied coated with spherical beads having a range in size from 15 micron to 45-micron beads. Here, many 15 micron beads are often located adjacent to a few 45 micron beads in a typical coated abrasive article. The exact size range of the 3-micron classification abrasive diamond particle supplied within the composite agglomerate beads coated on a commercially available abrasive article is typically not listed in the product literature description. The “3 micron” classification diamond particles are actually a range of particle sizes, with a distribution where some of the individual diamonds either larger or smaller than the nominal or average 3-micron stated size.
Abrasive beads having sizes of 45 microns or larger can be coated in single or mono layers on an abrasive article backing and used for abrading or lapping. Typically, the individual particles are worn down from their apex-top until only a small portion of each particle remains at the end of the life of the abrasive article. Individual particle are attached to a backing sheet with enough room between particles that each individual particle is in a highly localized pressure contact with a workpiece surface during an abrading process. The localized pressure on the exposed tip of an individual diamond particle is so high and the frictional heating of the particle tip due to abrading action so severe, that carbides can be formed when the carbon in the diamond combines with the iron in a steel workpiece. Formation of the carbides result in dulled diamond particles. If the spacing between the abrasive beads is too small, the abrasive article surface can actually act as a bearing surface rather than an abrading surface with little resultant abrading action that removes workpiece surface material. When abrasive particles are used, the scratched depth or material removed as a layer from a workpiece substrate is thought to be roughly proportional to the diameter or size of the particle. Large diameter particles are used to aggressively remove large quantities of workpiece material but they leave large scratches on the surface of the workpiece that result in a coarse or rough surface finish. Progressively smaller sized abrasive particles are used to effect a smooth surface as the scratches produced are also progressively smaller and the top “surface damage” produced by the previous larger sized particle is removed by the subsequent small particles. When the size of the particles are less than 20 microns or 10 microns and particularly, when less than 1 micron, the small quantity of abrasive particles contained in a monolayer coated on a backing prevents extended use of the abrasive article. This thin layer of abrasive particles coated would be worn away and expelled from the article surface rendering the abrading performance of the article ineffective. It has been found by the abrasive industry that the small sized particles desired to produce a smooth workpiece surface finish can be joined together in composite agglomerates having an eroding matrix of supporting porous ceramic material provides long abrading life of the article and produces a smooth workpiece surface finish. The eroding mixture is controlled to erode away at a rate where the individual particles become loosened and are expelled from the agglomerate at the time that the particles become dull from abrading. A fresh new layer of sharp particles is then provided to be in contact with the workpiece surface. The eroding process continues progressively from the top of the agglomerate to the bottom of the agglomerate until all of the volume of the agglomerate is worn away and all of the individual abrasive particles are used. Composite agglomerates have a typical size of 45 microns or less for a mixture of 3 micron or less sized abrasive particles. The 45 micron agglomerates are often spherical shaped ceramic beads where the 45 micron size is not too large that enough wear occurs on one portion of the abrasive article that the flatness of the abrasive article is unacceptable due to the agglomerate abrasive height change that occurs when only some of the agglomerates are worn down and other agglomerates have little wear. Within a typical 3 micron categorized ceramic bead agglomerate, the abrasive particle component of the agglomerate bead is not restricted only to particles that are exactly 3 microns in size as it is not practical to procure a quantity of a single size particle only.
When small particles are mixed with large particles, the adjacent large and small particles contained in a individual agglomerate will tend to produce different polishing effects simultaneously on the workpiece. The size of the agglomerates used to encase a specific particle size depends on many variables including the techniques or processes used to manufacture the ceramic beads or other types of agglomerates. Typically, the agglomerates coated on an abrasive article rated as “3 micron particles” have a range in size from a desired 45 micron size down to a small 15 micron size. All of the beads, independent of bead size, tend to have the same spherical shape. When 15 micron diameter beads are coated adjacent to 45 micron beads, the 15 micron beads would have little, if any, abrasive utility as they would only come into contact with the workpiece surface after a full 30 micron wear-down had occurred in the larger 45 micron beads. Only after this 30 micron amount of wear-down occurred would the smaller 15 micron beads start their abrading action.
Two common types of abrasive articles that have been utilized in polishing operations include bonded abrasives and coated abrasives. Bonded abrasives are formed by bonding abrasive particles together, typically by a molding process, to form a rigid abrasive article. Coated abrasives have a plurality of abrasive particles bonded to a backing by means of one or more binders. Coated abrasives utilized in polishing processes are typically in the form of circular disks, endless belts, tapes, or rolls that are provided in the form of a cassette. Individual abrasive particles can be attached to a backing by plating or by resin coating. However, if a mono or single layer of very small 1-micron (0.000039 inch) particles is coated on a backing sheet these small particles would typically wear out very quickly during the workpiece lapping or grinding process and the abrasive sheet article would be rendered useless. Variations in the thickness of abrasive disk articles and variations in the flatness of rotating platens prevent the effective use of small particles coated directly onto backing sheets. Also it would be necessary to have a super precision flat platen when these small 1 micron (0.000039 inch) abrasive particles, would be coated as a monolayer on a 30.5 cm (12 inch) diameter abrasive sheet disk article and the abrasive disk rotated at 3,000 rpm. Here, the rotating platen that is typically used in high speed lapping would have to have a dynamic flatness of much less than 1 micron total flatness variation across the contacting abrasive surface across in order for all of the moving abrasive particles to contact the workpiece surface. It is not practical to provide this high level of dynamic platen flatness on a lapping machine without great expenditures on the machine platen rotational spindle. The alternate method to utilize the small 0.1 to 15 micron abrasive particles for an fixed-abrasive lapping or polishing process has been to form larger composite agglomerates having a sufficient number of these small abrasive particles mixed with an erodible material and to coat these agglomerate beads on a backing sheet. The agglomerates contain a sufficient number of abrasive particles to provide a long abrasive coated article grinding life. However, the agglomerates are typically limited in size to 45 microns. If the size of the agglomerates is excessive, then it is difficult to evenly wear down all of the abrasive across the width of the surface of a workpiece resulting in the loss of workpiece surface flatness during the abrading process. A balance is sought in selection of the size of the agglomerate bead, the size range of abrasive particles contained within the agglomerate, the dynamic flatness of the platen and the required flatness of the workpiece.
Abrasive agglomerates are preferred to be spherical in shape and to be of a uniform size for precision lapping of workpieces. These spherical abrasive agglomerates are referred to here as abrasive beads or beads. If undersized beads are mixed with full sized beads and coated on the surface of abrasive articles, the undersized beads are often not used in the abrading process as they are too small to come into contact with a workpiece surface. This means also, that the expensive materials commonly used in including diamond particles, are wasted as they are not used.
Presently there are a number of methods used to manufacture abrasive beads. These beads have been used for many years in fixed abrasive articles, particularly those abrasive sheets used for lapping. However, there is a undesirable large variation in size of the beads produced, and used in the abrasive articles, with all of the present manufacturing methods. Abrasive manufactures seem reluctant to discard undersized beads because of the economic loss associated with expensive abrasive materials such as diamond and cubic boron nitride (CBN). Also, there is a cosmetic factor in that an abrasive article appears to contain more abrasive if the small undersized beads are also coated onto the abrasive article even if they will never be used in the abrading process. Among the earliest processes of making beads is a process developed by Howard in U.S. Pat. No. 3,916,584 where he poured a slurry mixture (of abrasive particles mixed in a Ludox® solution of colloidal silica suspended in water) into a dehydrating liquid including various alcohols or alcohol mixtures or heated oils including peanut oil, mineral oil or silicone oil and stirred it. Abrasive slurry droplets were formed into spheres by slurry-drop surface tension forces prior to the spheres becoming solidified by the water depleting action of the dehydrating liquid on the individual spheres. Smaller sized spherical bead sizes are produced by faster stirring of the dehydrating fluid. Beads vary in size considerably, with a batch of beads produced typically having a ten to one range in size. For instance, one batch produced a size range from 10 to 100 microns and as Example 1 produced beads having a range of from 20 to 200 microns. The U.S. Pat. No. 3,916,584 beads are used to compare the performance of abrasive beads produced by other bead manufacturing process techniques. Adefris, et al., in U.S. Pat. No. 6,645,624 discloses the manufacturing of spherical abrasive agglomerates by use of a high-speed rotational spray dryer to dry a sol of abrasive particles, oxides and water. Bitzer, in U.S. Pat. No. 4,364,746 discloses the use of composite abrasive agglomerates grains which are produced by processes including a fluidized spray granulator or a spray dryer or by agglomeration of an aqueous suspension or dispersion. Hampden-Smith, in U.S. Patent Application No. 2002/0003225 A1 and U.S. Pat. No. 6,602,439 produces abrasive beads by introducing slurry liquid onto the surface of an ultrasonic head operating at 1.6 MHz (1.6 million cycles per second) to produce 2 micron or smaller droplets.
Another method is described here for the manufacture of equal sized abrasive beads that can be used for abrasive articles. Here, droplets of an abrasive slurry are formed from individual mesh screen cells that have cell volumes that are equal to the desired droplet volumetric size. Screens that are commonly used to size-sort 45 micron (or smaller) particles can be used to produce liquid slurry droplets that are individually equal-sized and that have an approximate 45 micron size. Larger mesh cell sized screens can be used to compensate for the heat treatment shrinkage of the beads as they are processed in ovens and furnaces. These uniform sized beads prevent the non-utilization and waste of undersized beads that are coated on an abrasive article. Further these equal sized beads have the potential to produce higher precision accuracy workpiece surfaces in flat lapping than can abrasive articles having surfaces coated with a mixture of different sized beads as the workpiece would always be in contact with the same sized beads, each having the same abrading characteristics. It is thought that small diameter beads will have different abrading characteristics, including rate of material removal, as compared to large sized beads, both at very low relative surface contact speeds of less than 1000 surface feet per minute when moving small workpieces, including fiber optic devices, relative to the abrasive article surface and also, at high flat lapping surface speeds of greater than 1000 surface feet per minute where typically, the workpiece is held in contact with a moving abrasive article. These equal sized abrasive beads can be used both for raised island abrasive articles and also, for coating the flat backing sheet surfaces of rectangular sheets of abrasive articles. Composite ceramic abrasive beads can be screened to a narrow size range before coating to effect abrading benefits including those described herein. Reducing the standard deviation in the size of abrasive beads is an important advancement in the production of abrasive articles. The variance in the size of beads can be further reduced by screen sifting processes. Smaller sized beads having small size variations can be effectively used in a variety of abrasive articles. A small change in the nominal bead size is not as important as having a uniform size to the beads that are bonded to an abrasive article.
There are a number of suppliers that sell different grades, types and sizes of diamond particles to abrasive article manufactures. Diamond particles are produced by various methods and these particles can be sorted into specific size ranges which may include particles that range for example from 30 to 10 microns, or from 15 to 2 microns, or simply 15 micron and smaller. When composite agglomerates of diamond particles are produced, the basic component of diamond particles will include a prescribed range of particle sizes, all of which particle sizes are mixed with an erodible material including ceramics and encapsulated within a typical composite agglomerate particle. It is necessary that the size of the agglomerate bead is larger than the largest diamond particles that are enclosed within the bead. It is desired that many individual abrasive particles are contained within a individual agglomerate bead to allow the erodible agglomerate surface to be eroded away by abrading contact with a workpiece to expose the sharp surface of one or more hard abrasive particles that removes material from the contact surface of the workpiece as the abrasive moves in contact with the workpiece. Further abrading action will dull the edges of the exposed individual abrasive particles contained within the structure of the bead and as the erodible agglomerate bead material erodes away, the dull abrasive particles are ejected from the agglomerate and new sharp abrasive particles are exposed to continue the abrading action that removes material from the workpiece. Large abrasive particles abrade away more workpiece material than small particles but the large particles produce a less-smooth workpiece surface than do small abrasive particles. Use of a wide range of different sized individual particles contained within an agglomerate composite structure is thought to produce a smoother workpiece surface finish than will be produced by use of a very narrow range of abrasive particle sizes. Examples of commercially available polishing products include “IMPERIAL” Microfinishing Film (hereinafter IMFF) and “IMPERIAL” Diamond Lapping Film (hereinafter IDLF), both of which are commercially available from Minnesota Mining and Manufacturing Company (hereinafter 3M), St. Paul, Minn. The IDLF product line of abrasive articles include abrasive articles having spherical bead composite agglomerates coated on the backing film sheet has been commercially available for a number of years.
Many different coating techniques can be used to resin coat a flexible backing sheet with abrasive beads. One technique includes a method to coat a slurry mixture of abrasive beads and a polymer resin on the surface of a backing with process procedures to create a mono or single layer of abrasive particles or agglomerates on the surface of a backing. Another technique includes a method where a thin coat of polymer resin is coated on a backing and abrasive beads are drop coated or propelled to the surface of the resin coating by electrostatic or other techniques. Other resin coatings may be applied to the attached particles including size coatings that strengthen the bond of the individual particles to the backing for increased resistance to the abrading forces that tend to dislodge the particles from the backing surface. When organic or polymer binders are used to bond abrasive particles to a backing sheet the particles are often mixed in a resin slurry that is commonly referred to as a binder precursor that is a binder that is in a liquid or flowable state. After the resin slurry, or resin, is coated on an abrasive article the resin is cured or polymerized to create a binder that is in a solid, non-flowable state thereby fixturing the abrasive particles to the backing sheet.
Abrasive media may require surface conditioning prior to use to remove “high-riser” abrasive beads. Also, when the spherical bead type enclosed body composite agglomerate is bonded to an abrasive article backing, it is necessary to first break the spherical exterior surface of the agglomerate to expose individual sharp edged abrasive particles for use in abrading the surface of a workpiece. The constituent volumetric percentage amount of diamond or other particles used in the agglomerate binder mixture affects the performance of the abrasive article. Composite abrasive agglomerate coated abrasive articles have been marketed for years including those using ceramic and metal oxide encased composite spherical beads that are offered with a variety of size classifications of diamond abrasive particle sizes.
U.S. Pat. No. 794,495 (Gorton) discloses dots of abrasive on round disks formed by depositing abrasive particles on adhesive binder wetted dot areas printed on the backing, primarily to aid the free passage of grinding debris away from the workpiece surface. These dot areas are not elevated as raised island shapes from the surface of the backing.
U.S. Pat. No. 1,657,784 (Bergstrom) describes flat surfaced island-type rectangular sheet abrasive articles having different geometric patterns of island shaped abrasive areas.
U.S. Pat. No. 1,896,946 (Gauss) describes raised island-type abrasive articles having a array of abrasive blocks attached to a thin flexible base that allows each island abrasive block to move independent of the other adjacent blocks.
U.S. Pat. No. 1,924,597 (Drake) describes flat surfaced island-type abrasive disk articles.
U.S. Pat. No. 1,941,962 (Tone) describes flat surfaced island-type abrasive rectangular articles having alternating bars of abrasive.
U.S. Pat. Nos. 2,001,911 and 2,115,897 (Wooddell, et. al) describes raised island-type abrasive disks and other articles.
U.S. Pat. No. 2,108,645 (Bryant) describes raised island-type rectangular abrasive articles.
U.S. Pat. No. 2,216,728 (Benner et al.) discloses a porous composite diamond particle agglomerate granule comprised of materials including ceramics and a borosilicate glass matrix that can be fired in an oxidizing atmosphere at 600 degrees C. and then fired at 900 degrees C. in a reducing atmosphere. Diamonds are subject to oxidization at temperatures above 700 degrees C. so a non-oxidizing atmosphere is used up to 1500 degrees C.
U.S. Pat. Nos. 2,242,877, 2,252,683 and 2,292,261 (Albertson) describes raised island-type abrasive disk articles. A thick coating of adhesive is applied to a disk backing and abrasive particles are deposited on the adhesive surface. Then an island cavity embossing tool is forced against the abrasive coated surface to create a pattern of raised islands. It is necessary to have a thick under-layer of adhesive so that the leading edge of the embossing tool can route some of the adhesive from the leading edges of the embossing tool upward into the raised-island pockets in the embossing tool. If a thin layer of adhesive is used, the embossing tool would simply “bottom-out” when the surface abrasive particles are pushed by the tool leading edges directly in contact with the backing surface with little or no lateral flow of adhesive from the leading edges of the embossing tool into the raised-island cavities of the tool. Generally, for the production of modern conventional abrasive media where an abrasive backing article having drop or electrostatic coated abrasive particles, the backing has an adhesive coating that is less thick than the diameters of the individual abrasive particles. This thin adhesive coating allows the particles to penetrate only one half of their diameter, or less, into the adhesive which results in exposure of about one half of the particle surface above the adhesive layer to provide effective abrasive grinding. Here, as disclosed in Albertson, the individual abrasive particles contained in the abrasive layer are driven down into the adhesive layer, at the leading edges of the embossing tool (which form the valleys between the raised island structures). If the adhesive layer is thin, the embossing tool leading edge will contact the top surface of the abrasive particles which would be driven into contact with the backing surface and no sideways motion would be imparted to the adhesive fluid which resides in the regions between the individual abrasive particles. The particles act as bridges for the contained adhesive fluid. With thin adhesive coatings, it is not possible to create a valley in the adhesive/abrasive mixture, and also, it would not be possible to create raised island structures from the mixture. The only way to create island structures from this type of coating is to have an adhesive layer that is considerably thicker than the diameter or height of the abrasive particles. The adhesive thickness must also be greater than the depth of the island-cavity pockets in the embossing tool or the island cavities of the tool will not be filled when the tool is pressed into the abrasive/adhesive mixture. When the embossing tool is pressed into the mixture the abrasive particles contained on the surface of the raised islands are also forced into the adhesive layer. Further, the abrasive particles located at that raised island top-surface location are also mixed with adhesive, internal to the island structure, due to the fluid flow shearing action of the adhesive/abrasive-particle mixture as the mixture is moved from the regions of the island valleys to the raised island top surfaces. Raised islands can be made quite high and the abrasive article coatings can be made to reside as a near-single layer on top of the island structures with the proper design of the embossing tool, the control of the adhesive viscosity and the thickness of the adhesive, the selection of the abrasive particle size and the design of the embossing technique. It would be difficult to get each island cavity completely filled with the polymer mixture as air would be trapped to form air voids at the top of each cavity as the embossing tool is advanced into the abrasive/adhesive mixture. Withdrawal of the embossing tool before solidification of the polymer adhesive would distort each island structure, as the adhesive would tend to adhere to the embossing cavity walls as the tool is moved away from the embossed islands. There is no teaching of the control of the height of each abrasive covered island relative to the backside of the disk backing. Condensation type phenolic thinned with solvents are used as a adhesive binder. FIGS. 1, 2 and 3 (Prior Art) show different views of the Albertson raised island shapes and raised island disks. FIG. 1 (Prior Art) is a cross section view of abrasive particle coated raised islands that are formed by pressing an embossing tool into a composite fluid of a thick under-layer of adhesive that was applied to a backing disk sheet where the adhesive is over-coated with abrasive particles. A disk backing 10 has raised island structures 12 and island recessed channels 13 that are coated with abrasive particles 14. The height of the islands 12 is measured from the backside of the backing 10 by the island height distance 16. FIG. 2 (Prior Art) is a top view of raised islands on an abrasive disk. The abrasive disk 18 has an aperture center hole 22 and abrasive coated raised island structures 20, 23 and 25. The disk 18 backing 17 has partial-sized island structures 23 and 25 that are located on the periphery of the disk 18. The reduced-sized islands 23, 25 can be structurally unstable during abrading usage, as the attachment base area of each of these small islands 23, 25 that are attached to the backing 17 can be small as compared to the base area of a full sized island 20. These islands 23, 25 that are located on the disk 18 periphery are particularly sensitive structurally when subjected to abrading leveraging forces for tall-height islands. Undersized islands, having small base areas that are located in a more interior portion of the disk 18 can also be structurally weak if the height of the small islands, measured from the top of the island to the top surface of the backing 17, is large relative to the base area or the base area dimensions. Albertson does not discuss the use of full sized islands 20 in all areas of the disk 18 including the peripheral edge area of the disk 18. FIG. 3 (Prior Art) is a cross section view of a pattern of rectangular shaped raised rib structures that are formed on a disk surface after which the raised rib structures are over-coated with an abrasive/adhesive mixture coating to provide a disk with a pattern of raised island ridges and adjacent grooves as shown in FIG. 23 of Albertson U.S. Pat. No. 2,242,877. A disk backing 26 has attached raised island structures 24 that are coated with an abrasive particle 29 and adhesive 28 mixture, where the height of the abrasive particle 29 and adhesive 28 mixture islands 24 is measured from the backside of the backing 26 to the top of the abrasive particles 29 by the distance 30. FIG. 10 (Prior Art) shows a side view of an abrasive grinding disk that is mounted on a mandrel tool that is used to grind a workpiece with the grinding abrasive disk distorted as it contacts a workpiece surface. This type of abrasive disk article is suitable for rough grinding but lapping can not be accomplished when using it as the raised islands on a angled disk that first come in contact with a flat workpiece tend to scratch the workpiece rather than polish it. This type of manual tool disk article is disclosed in U.S. Pat. Nos. 2,242,877, 2,252,683 and 2,292,261 by (Albertson), U.S. Pat. No. 3,498,010 (Hagihara), U.S. Pat. No. 3,991,527 (Maran) and U.S. Pat. No. 6,371,842 (Romero). A mandrel tool 108 has a disk aperture hole mounting hub 110 that attaches both the flexible tool pad 118 and the abrasive disk 120 to the tool 108. The disk 120 has attached raised islands 112 that are surface coated with an abrasive coating 114 where a leading-location island 112 abrasive coating 114 contacts a workpiece 122 at a abrasive contact point 116.
U.S. Pat. No. 2,755,607 (Haywood) describes abrasive coated articles having a pattern of raised adhesive shapes that are formed on a backing and the raised shapes are then coated with abrasive particles on a continuous web basis to form rectangular shaped abrasive articles.
U.S. Pat. No. 2,838,890 (McIntyre) describes abrasive coated articles having a pattern of backing sheet through holes for the abrasive debris to escape the abrading area.
U.S. Pat. No. 2,907,146 (Dynar) describes raised island-type abrasive disk articles.
U.S. Pat. No. 3,048,482 (Hurst) describes raised island-type abrasive disk articles.
U.S. Pat. No. 3,121,298 (Mellon) describes raised island-type abrasive disk articles. Recessed channels are provided on a backing sheet, the sheet is adhesive coated and abrasive particles are deposited on top of the adhesive to create a abrasive disk that has raised island structures top surface coated with abrasive particles.
U.S. Pat. No. 3,423,489 (Arens, et al.) discloses a number of methods including single, parallel and concentric nozzles to encapsulate water and aqueous based liquids, including a liquid fertilizer, in a wax shell by forcing a jet stream of fill-liquid fertilizer through a body of heated molten wax. The jet stream of fertilizer is ejected on a trajectory from the molten wax area at a significant velocity into still air. The fertilizer carries an envelope of wax and the composite stream of fertilizer and wax breaks up into a string of sequential composite beads of fertilizer surrounded by a concentric shell of wax. The wax hardens to a solidified state over a free trajectory path travel distance of about 8 feet in a cooling air environment thereby forming structural spherical shapes of wax encapsulated fertilizer capsules. Surface tension forces create the spherical capsule shapes of the composite liquid entities during the time of free flight prior to solidification of the wax. The string of composite capsule beads demonstrate the rheological flow disturbance characteristics of fluid being ejected as a stream from a flow tube resulting in a periodic formation of capsules at a formulation rate frequency measured as capsules per second. Capsules range in size from 10 to 4000 microns.
U.S. Pat. No. 3,495,362 (Hillenbrand) describes island-type abrasive disk articles having a thick backing, a disk-center aperture hole and raised abrasive plateaus.
U.S. Pat. No. 3,498,010 (Hagihara) describes island-type abrasive disk articles having a thick backing, a disk-center aperture hole and the backing having patterns of attached raised island structures formed on the backing surface. The islands are mold formed from a mixture of abrasive particles and a phenolic resin. The abrasive disks are used on manually operated portable grinding tools that are shown to distort the abrasive disk article out-of-plane when held with force against a workpiece surface. Comparative tests indicated that the disks had superior material removal rates and produced very smooth finishes as compared to tradition abrasive disks. The disks are very stiff after manufacture so they are subjected to a rotary device that cracks the disk in many places to provide flexibility of the thick disk. FIG. 11 (Prior Art) shows a cross section view of a disk that is in abrading contact with a workpiece. The abrasive disk 100 is shown by Hagihara to be in abrading contact with a workpiece 106 where the disk abrasive islands 102 and 104 contact the workpiece 106 on the island edges rather than the islands laying in flat contact with the workpiece 106.
U.S. Pat. No. 3,517,466 (Bouvier) describes raised abrasive cylinders mounted on a disk plate.
U.S. Pat. No. 3,605,349 (Anthon) describes raised abrasive islands on an abrasive backing article.
U.S. Pat. No. 3,702,043 (Welbourn et al.) describes a machine used for removing material from the internal surface of a workpiece and the use of a strain gage sensor device that indicates the cutting force exerted by the cutting tool upon the workpiece.
U.S. Pat. No. 3,709,706 (Sowman) discloses solid and hollow ceramic microspheres having various colors that are produced by mixing a aqueous colloidal metal oxide solution, that is concentrated by vacuum drying to increase the solution viscosity, and introducing the aqueous mixture into a vessel of stirred dehydrating liquid, including alcohols and oils, to form solidified green spheres that are fired at high temperatures. Spheres range from 1 to 100 microns but most are between 30 and 60 microns. Smaller sized spheres are produced with more vigorous dehydrating liquid agitation. Another sphere forming technique is to nozzle spray a dispersion of colloidal silica, including Ludox, into a countercurrent of dry room temperature or heated air to form solidified green spherical particles.
U.S. Pat. No. 3,711,025 (Miller) discloses a centrifugal rotating atomizer spray dryer having hardened pins used to atomize and dry slurries of pulverulent solids.
U.S. Pat. No. 3,859,407 (Blanding et al.) discloses a system of producing shaped abrasive particles by supplying a stream of a plastically formable abrasive mixture into a nipped set of rolls, where one or more of the rolls has a surface pattern of geometric shapes that the formable material is squeezed into as the rolls rotate. A continuous ribbon of the individual shaped abrasive particles that are joined together at the formed particle shape edges exits the rolls. The ribbon is flexed after the particles are solidified to separate the ribbon into individual particles.
U.S. Pat. No. 3,916,584 (Howard, et al.), herein incorporated by reference, discloses the encapsulation of 0.5 micron, or less, up to 25 micron diamond particle grains and other abrasive material particles in spherical erodible metal oxide composite agglomerates ranging in size from 5 to 200 microns and more. The large agglomerates do not become embedded in an abrasive article carrier backing film substrate surface as do small abrasive grain particles. In all cases, the composite bead is at least twice the size of the abrasive particles. Abrasive composite beads normally contain about 6 to 65% by volume of abrasive grains, and compositions having more than 65% abrasive particles are considered to generally have insufficient matrix material to form a strong acceptable abrasive composite granule. Abrasive composite granules containing less than 6% abrasive grains lack enough abrasive grain particles for good abrasiveness. Abrasive composite bead granules containing about 15 to 50% by volume of abrasive grain particles are preferred since they provide a good combination of abrading efficiency with reasonable cost. In the invention, hard abrasive particle grains are distributed uniformly throughout a matrix of softer microporous metal oxide (e.g., silica, alumina, titania, zirconia, zirconia-silica, magnesia, alumina-silica, alumina and boria, or boria) or mixtures thereof including alumina-boria-silica or others. Silica and boria are considered as metal oxides. The spherical composite abrasive beads are produced by mixing abrasive particles into an aqueous colloidal sol or solution of a metal oxide (or oxide precursor) and water and the resultant slurry is added to an agitated dehydrating liquid. Examples teach the use of a slurry mixture of abrasive particles mixed in a Ludox® solution of colloidal silica suspended in water. Dehydrating liquids include partially water-miscible alcohols or 2-ethyl-1-hexanol or other alcohols or mixtures thereof or heated mineral oil, heated silicone oil or heated peanut oil. The slurry forms beadlike masses in the agitated drying (dehydrating) liquid. Water is removed from the dispersed slurry and surface tension draws the slurry into spheroidal composites to form green composite abrasive granules. Other shapes than spheroidal such as ellipsoid or irregularly shaped rounded granules can be produced that also provide satisfactory abrasive granules. The green granules will vary in size; a faster stirring of the drying liquid giving smaller granules and vice versa. The resulting gelled green abrasive composite granule is in a “green” or unfired gel form. The dehydrated green composite generally comprises a metal oxide or metal oxide precursor, volatile solvent, e.g., water, alcohol, or other fugitives and about 40 to 80 weight percent equivalent solids, including both matrix and abrasive, and the solidified composites are dry in the sense that they do not stick to one another and will retain their shape. The green granules are thereafter filtered out, dried and fired at high temperatures. The firing temperatures are sufficiently high, at 600 degrees C. or less, to remove the balance of water, organic material or other fugitives from the green composites, and to calcine the composite agglomerates to form a strong, continuous, porous oxide matrix (that is, the matrix material is sintered). The resulting abrasive composite or granule has a essentially carbon-free continuous microporous matrix that partially surrounds, or otherwise retains or supports the abrasive grains. The firing temperatures are insufficiently high to cause vitrification or fusion. Vitrification of the composite agglomerate or granule is avoided as the external surface of the composite would change into a continuous glassy state, thereby preventing the composite from having a porous external surface. Some example abrasive agglomerates using Aluminum oxide abrasive particles were fired at 700 degrees C. which produced a smooth, shiny agglomerate surface finish. The green-state beads that are fired at up to 600 degrees C. typically shrink the green-state beads by from 10 to 20 percent. Having a porous surface on abrasive agglomerates allows liquid adhesive binders to penetrate the porous agglomerate surface somewhat or to better wet the agglomerate surface that tends to provide increased bonding strength when the agglomerate is attached to the surface of a backing sheet. The spherical composite matrix outer surface retains a degree of micro-porosity, as can be detected by the disappearance of the matrix when the spherical composite is filled with oil having the same refractive index as the matrix where the oil penetrates into the porous matrix. When the oil filled composite agglomerate is viewed with an optical microscope, only the diamond grains are visible and the dispersion of the diamond particles within the agglomerate can be seen. This oil-absorbing feature of the matrix spherical composite permits the incorporation of liquids including lubricants, liquid grinding aids, etc., to enhance performance of the composite in actual abrading operations. The sintering temperature of the whole spherical composite bead body is limited as certain abrasive granules including diamonds and cubic boron nitride are temperature unstable and their crystalline structure tends to convert to non-abrasive hexagonal form at temperature above 1200 degree C. to 1600 degrees C., destroying their utility. An air, oxygen or other oxidizing atmosphere may be used at temperatures up to 600 degrees C. but an inert gas atmosphere may be used for firing at temperatures higher than 600 degrees C. The Ludox® colloidal solution provides the metal oxide that forms a porous oxide structure that surrounds the individual abrasive particles within the abrasive agglomerate bead. These abrasive composite agglomerate beads incorporate abrasive particles 25 microns and less sized particles, as abrasive particle grains 25 microns and larger can be coated on abrasive articles to form useful materials. Example 1 described a mixture of 0.5 gram of 15-micron diamond powder, 3.3 grams of 30 percent colloidal silica dispersion in water (Ludox LS) and 3 grams of distilled water that was stirred and sonically agitated to maintain a suspension. The formed agglomerates were fired, a backing sheet was coated with a make coat of phenolic resin, and the abrasive spherical agglomerates were drop coated onto the wet resin and the excess of the spherical agglomerates were allowed to fall off. Applying the abrasive spheres to the abrasive backing sheet by this technique results in a abrasive article that has essentially a 100% coating of abrasive spheres with little or no space between individual adjacent abrasive spheres. After heating the abrasive coated backing sheet to precure the phenolic make coat, a size coat of the same resin was applied to the coated spherical agglomerates and the abrasive sheet article was further heated to fully cure the resin. Then this abrasive sheet article was formed into a disk and used to for forming and polishing workpieces with the result that this 100% abrasive spherical bead coated article showed a 30-40% higher rate of cut and provided a better surface finish than a conventional 15 micron (micrometer) diamond coated abrasive disk sheet article. It is significant that this comparative test shows that when small abrasive particles are formed into erodible ceramic agglomerate spheres that are coated on a backing sheet, it is not necessary to have a minimum separation between each of the adjacent abrasive spheres to obtain workpiece high cut rates and smooth surfaces. In other workpiece abrading applications where diamond abrasive particles are coated on a backing sheet with little or no space between adjacent individual abrasive particles, the cut rate can be reduced significantly compared to an abrasive article having gap spaces between adjacent abrasive particles. The uniform (non-gap-space) abrasive particle coating can act as a bearing surface for a workpiece rather than a cutting surface. Example 8 resulted in composite granules that ranged in diameter from 10 to 100 microns, with an average of about 50 microns and the diamond particle content was approximately 33% of the abrasive composite agglomerates. In example 6, a slurry of the average sized 50 micron abrasive agglomerates was mixed in a phenolic resin and was knife coated with a 3 mil (0.003 inch or 72 micron) knife gap setting which exceeded the size of the agglomerates. In Example 9, beads were screened to be less than 30 microns (0.0012 inches) in size before mixing them in a binder which was coated on a 0.003 inch (75 micron) thick polyester backing sheet using a coating knife opening of 0.002 inches (50 microns) which allowed the beads to pass through the knife opening gap. As the individual abrasive particles were smaller than the depth of the coated resin binder slurry (where the coating depth is approximately equal to the knife opening gap setting), there is indication that enough resin binder solvent was evaporated after coating to expose a substantial portion of the individual coated abrasive agglomerates when the abrasive product was dried. In Example 1, a backing sheet was coated with a wet make-coat binder and abrasive beads was dropped on the make coat and the excess of beads was allowed to fall off the backing. This type of abrasive coating will produce a uniform layer of abrasive beads across the full surface of the make-coat wetted surface of the backing with little or no spacing between adjacent individual abrasive agglomerate beads. Typically, a abrasive sheet article is not coated with a uniform continuous coating of individual abrasive non-agglomerate particles as the densely packed abrasive will not abrasively remove workpiece material in an aggressive fashion. Instead, the continuous abrasive particle covered surface can tend to act as a bearing surface that supports rather than abrades a workpiece. However, comparative tests of the densely-packed agglomerate bead covered surface showed a 30-40 percent higher rate of cut and provided a better surface finish than a comparative conventional abrasive article. When a composite bead granule was submerged in oil having a refractive index of about 1.5 under a microscope at 70-140× the oils penetration into the porous matrix was observed by visual disappearance of the silica matrix and only diamond particle grains throughout the composite bead granule were readily visible. The dispersion of the diamond particle grains throughout the bead granule was noted.
U.S. Pat. No. 3,921,342 (Day) discloses a lapping plate that has raised island sections where an abrasive liquid can flow in the recessed channel areas.
U.S. Pat. No. 3,933,679 (Weitzel et al.) discloses the formation of uniform sized ceramic microspheres having 1540 microns and smaller ideal droplet diameters. Mechanical vibrations are induced in an aqueous oxide sol-gel fluid stream to enhance fluid stream flow instabilities that occur in a coaxial capillary tube jet stream to form a stream of spherical droplets. Droplets are about twice the size of the capillary orifice tube diameter and the vibration wavelength is about three times the diameter of the tube. The spherical oxide droplets are solidified in a dehydrating gas or in a dehydrating liquid after which the solidified droplets are sintered. The spherical metal oxide particles have a very narrow-size distribution. Reference is made to alternative droplet generators such as spray nozzles, spinning discs and bowls that provide feed stock dispersion at high throughput capacity but these devices produce an undesirably wide droplet size distribution. Generally this vibration enhanced spherical droplet system is effective for making larger sized spheres with the use of capillary tubes having diameters of approximately 630 microns (0.024 inches). The production of 45-micron spheres would require a capillary tube diameter of only 23 microns (0.0009 inches) that is too small for practical use in the production of significant quantities of oxide spheres. Example 2 indicated extreme accuracy in control of the sphere sizes in that 99% of the large sized 599 micron (0.024 inch) microspheres produced had sphere diameters within the relatively narrow range of 0.43 microns (0.000017 inch).
U.S. Pat. No. 3,991,527 (Maran) describes abrasive disk articles having disk-center aperture holes that are used on manual mandrel abrading tools. Geometric patterns of island structures are formed on the surface of a disk backing sheet where the island structures have individual flat top surfaces and recessed valley areas around each raised island structure. The island surfaces are coated with a phenolic or other polymer resin but the recessed valley areas are left adhesive-free. Abrasive particles are then applied (only) to the resin adhesive coated island surfaces to form a abrasive disk that has the top flat surfaces of each individual island coated with abrasive particles while the recessed valley areas that exist between the raised island structures remains free of abrasive particles. Maran describes an electrostatic abrasive particle deposition apparatus. FIG. 4 (Prior Art) is a cross section view of the abrasive coated raised island structures. The abrasive disk 48 has raised island structures 44 that are coated with a layer of adhesive 42 that bonds abrasive particles 36 to the abrasive top-surface 38 of the raised island structures 44. Each of the raised island structures 44 have uncoated island recessed channel areas 40 that are located between the raised islands 44. There is no described control of the height 46 of the individual abrasive 36 coated islands 44 as measured from the island-top abrasive surfaces 38 to the backside of the disk 48 backing. FIG. 5 (Prior Art) is a top view of the Maran abrasive disks having geometric patterns of raised island structures. The disk 54 has raised islands 50, 53 and 58 and recessed channel areas 52 between the islands 50, 53 and 58. The island 50 is a full-sized island and the islands 53 and 58 are diminished-sized islands that are located on the periphery of the disk 54. Maran does not discuss the use of full sized islands 50 in all areas of the disk 54 including the peripheral edge area of the disk 54. The disk 54 has a disk-center aperture hole 56 that is used to mount the disk 54 to a manual tool mandrel, not shown. The recessed channel areas that exist between the islands are coplanar with the island top surfaces and are used to scavenging grinding debris from the abrading contact area with a workpiece as the debris is thrown out of the recessed channels at the periphery of the abrasive disk. No mention is made of the use of islands and recessed areas between the islands to break up the water coolant boundary layer that forms between a workpiece flat surface and a abrasive article abrasive surface during abrading.
U.S. Pat. No. 4,038,046 (Supkis) describes abrasive articles made with a blend of urea formaldehyde and alkaline catalyzed resole phenolic binder resins which are cured with the same curing time and temperatures as conventionally used for phenolic resins. Abrasive particles applied by gravity and also by electro-coating methods. A typical oven cure cycle of the web is 25 minutes at 125 degrees F., 25 minutes at 135 degrees F., 18 minutes at 180 degrees F., 25 minutes at 190 degrees F., 15 minutes at 225 degrees F. and 8 hours at 230 degrees F. Yellow and blue dyes are mixed in the binder system.
U.S. Pat. No. 4,111,666 (Kalbow) describes island-type abrasive articles having a foam backing that has island protuberances that are impregnated with polymer stiffening agent and the top island surfaces coated with a mixture of abrasive particles and a polymer adhesive.
U.S. Pat. No. 4,112,631 (Howard), herein incorporate by reference, discloses the encapsulation of 0.5 micron up to 25 micron diamond particle grains and other abrasive material particles in spherical composite agglomerates ranging in size from 10 to 200 microns. A liquid mixture of abrasive particles and a grinding aid is added into a stirred liquid mixture of a urea-formaldehyde which creates spheres of the abrasive-grinding aid which are encapsulated by a shell layer of the urea-formaldehyde material. The diameters of the spherical abrasive capsules ranged by a ratio of thirty to one as the individual abrasive agglomerate capsules ranged in size from 5 to 150 microns in Example 1. The polymer shells that surround the abrasive particles which are dispersed in the grinding aid material provide abrasive agglomerates that can be coated on an abrasive article. Encapsulated 75 micron composite spheres were knife-coated using a knife opening of 3 mils (76 micron) on a polyester film backing with a urethane phenoxy resin make coating that was thinned with methyl ethyl keytone.
U.S. Pat. No. 4,251,408 (Hesse) describes phenolic resins used in preparation of abrasives where rapid curing as a result of increasing the curing temperature tends to form blisters which impairs the adherence of the resin to the substrate backing. Special cure cycles are used which have low initial curing temperatures with regulated, progressively increasing temperature which prevent blister formation but the time required for cross-linking is thereby increased. Drying and curing of webs by use of loop dryers or festoon dryers are discussed which provide both the function of driving off the solvents from the binder and to cross-link cure the binder. The cure rate of a resin is defined by the B-time which is the time required to change from a liquid state to reach the rubbery elastomer state (B-state).
U.S. Pat. No. 4,256,467 (Gorsuch) describes an abrasive article with diamond particles plated onto an electrically insulated mesh cloth which can be cut into a “daisy wheel” for use in grinding curved, convex, or concave optical lenses. These articles are intended for rough grinding and not for lapping. An electrically conductive smooth metal cylindrical drum is coated with an insulating resist except in circular dot or spot areas where metal plating is desired. An electrically insulating woven cloth, typically made of common plastic fiber materials, is stretched over the whole drum surface including both the conductive spot areas and the resin insulated drum areas. The cloth covered drum is then placed in a plating tank and electroplating then starts where metal is plated through the cloth at the conductive spot areas. Buildup of plated metal occurs at the circular spots and electroplating continues until the desired plated metal thickness is reached to form raised islands that extend through the cloth thickness and above the curved cylindrical drum surface. Then small diamond particles are introduced into the electroplating bath liquid and plating continues, thereby trapping some of these diamond particles at the island top surface by metal electroplate bonding them to the exposed surface of the previously plated island areas. The plating action is stopped, the drum is removed from the bath and the cloth is separated from the drum surface to provide a cloth material having integral raised islands that have non-flat drum-cylinder shaped curved top surfaces that are covered with abrasive particles. The drum is described as being optionally rotated. After plating these diamond particles on the island top surfaces, the particles will all have different heights relative to the drum surface, and thus, relative to the bottom of the cloth due to a number of factors. It is well known that metal plating varies in thickness over different areas of a plated member simply due to variables inherent in an electro-plating process. Also, the woven cloth will have different thicknesses due to variations in the weaving machine performance. Also, there are variances in the thickness of individual woven cloth strands of the very fine denier fibers that are joined together to form a single strand. Further, the sleeve of material is stretched and pulled over the cylindrical drum, which can cause variations in the cloth thickness around the surface of the drum. All of these factors result in a flexible abrasive that can be cut into weak strips or legs that are fanned out from a common hub to form a daisy wheel article where the legs will conform to a curved lens when used at very low speeds. The individual stiff metal raised abrasive island structure surfaces of this daisy wheel will not locally conform, across the semi-rigid surface area of a typical metal plated flat abrasive island, to a curved lens surface. In fact, as the individual raised islands have the same curved surface shape as the drum surface, these island shapes will not lay in flat contact with a flat workpiece surface and also will not lay in conformance to a spherical lens curvature. Use of these stiff metal abrasive islands in abrading contact with the curved lens surface can result in abrading contact to be concentrated at a very small portion of a raised island structure. A plated metal portion of the island structure may contact the curved lens at a raised island location that does not contain abrasive particles, or it is possible that a single abrasive particle that is plated at the highest elevation of that portion of the raised island structure will alone contact the curved portion of the lens which will result in undesirable scratches of the lens surface by that single particle. This daisy wheel article is not useful for high speed lapping which requires extremely precise abrasive article thickness control. Again, in this patent, as was the case in his U.S. Pat. No. 5,318,604, he acknowledges and addresses the issue of obtaining an abrasive article that does, in fact, have all the abrasive particles in the same plane. This is done producing a cloth mesh island abrasive covered article with use of plastic cloth over a patterned drum. Here, he electroplates islands of metal over exposed areas and electroplates particles dropping out of the plating solution to these plated islands after which he continues to build up the metal plating thickness, add a cloth, continue plating, and then remove the cloth mesh from the drum. The islands are refereed to as having flat plane abrasive surfaces but island flat plane surface can not be produced from a cylindrical drum surface. The resultant article would seem to have little use as a abrasive article as the diamond particles are not exposed at the drum surface, but rather, are enclosed or buried within the plated metal layer by the progressively built-up plating metal. As they are not exposed from the plated metal surface, they cannot effect their abrasive cutting action. Also, the backside thickness of plated metal would vary in height due to variances in the deposition rate of material over each island site to variances in electrical conductivity of the unknown coating applied over each site which allows the plated metal to be peeled from the drum. When the cloth is turned over, and mounted to a backing, the variance in height of each island, as measured from the front surface of the diamonds to the cloth bonded surface of the backing, will be significant over the whole surface of the abrasive article. This abrasive article would have no use for high speed lapping where the high speed of a rotating platen establishes an abrasive sheet mounting flatness plane more precise as the platen rotation speed is increased. The requirements of high speed lapping far exceed the capability of this system of creating abrasive articles. In U.S. Pat. Nos. 4,256,467, 5,318,604, and 4,863,573 (Gorsuch and Moore) having metal island areas that are progressively built up by electroplating areas of cloth produce an aggressive grinding media that is not useful for precision polishing. The production process has many unique features that are reflected in the abrasive article finished product. Part of the process has cloth that is positioned in contact with an electrically insulated metal drum having arrays of exposed circular electrically conducting island-forming areas coated with wax. Abrasive particles contained in the electroplating liquid bath fall on the upper portion of the near-full-height plated metal islands during the process of depositing metal to create the islands. After the abrasive particles are metal bonded to the top surface of the islands that were formed by plating metal buildup, the island abrasive particle covered top surface curvature would tend to match the curvature of the circular drum. At completion of the plating process, the cloth encompassing the individual abrasive covered island structures is peeled from the drum surface and laid flat to be used, by further manufacturing steps, to create a variety of abrasive articles. However, the individual abrasive particles do not lie in a common flat plane. Instead, the particles are bonded on the curved surface of the raised islands, and also, are attached at many different random elevations within the upper portion of island structures. This particle out-of-flatness condition, where each particle is at a different elevation, occurs in part, because of uneven plated metal deposition rates that occur over the surface of the drum at all the different island locations during the process of building-up the height of each island. Also, a random uneven particle deposition occurs over time when particles come out of solution and are deposited in the final portion of the island build-up. Further, the plating process creates nominal island height differences that vary from island to island, in part, due to the different characteristics of the individual fibers of the mesh cloth. The height thickness of each island, as measured from the surface of the plated abrasive particles to the backside of the mesh cloth, or to the island bottom, is not precisely uniform. Another thickness tolerance disadvantage of this product occurs when the plated cloth material is stripped from the electrically conductive metal base and attached with adhesive to a backing substrate sheet to form a laminated abrasive article. This laminated abrasive article does not have precise overall thickness control due to thickness variations in the island plated cloth material, in the backing sheet, and in the laminating adhesive. The product can be used to create a flat workpiece surface by grinding action but is generally not effective for creating smooth surfaces, particularly in high speed lapping. The different height locations of the abrasive particles prevent the generation of precision workpiece smooth surfaces during abrading action. However, the plated abrasive island articles can be effective in producing flat (but not smooth) workpieces. Large abrasive particles, ranging from 100 to 300 microns, are preferred for plating. Segmented island areas consisting of abrasive particles dispersed in a resin binder that is directly molded on the surface of a backing, with grooves between the thick abrasive coated areas, is disclosed but these areas are not raised island areas. In another embodiment, a metal belt, used as a flat electrical conducting surface, is joined with a open mesh continuous web within an electroplating tank and abrasive covered raised islands are electroplate formed in patterns within the fiber mesh material that is separated from the belt and cut up or laminated into abrasive articles. Diamond particles can be surface coated with metals including copper, nickel, silver, cobalt and molybdenum and they can also coated with non-metals.
U.S. Pat. No. 5,318,604 (Gorsuch et al.) and U.S. Pat. No. 4,863,573 (Moore et al.) describes abrasive articles made by metal plating islands of which are top coated with diamond abrasives that have been plated onto the islands. The technique employed is to create an island by printing an insulation solder photo resist insulation pattern over an electrical conducting plate and overlaying this with a woven non-electrical conduction cloth mesh. When immersed in a plating bath, a metal plated island is formed integral with the cloth mesh over the electrically exposed island areas of the photo resist covered metal conducting plate. After a minimum height of metal plated island area is built up by metal progressively covering the island area of interlocking mesh fiber strands, diamond particles are suspended in the plating bath liquid and allowed to free fall by gravity onto the mesh. Those particles that fall into the small island areas, which are very irregular in shape due to the unevenness of the interlocking fibers, are progressively plated onto the existing metal plated surfaces. However, the individual plated abrasive particles do not lie in a common flat plane. Instead, the particles are electroplate bonded on the curved surface of the raised islands, and also, are attached at many different random elevations within the upper portion of island structures. This abrasive particle out-of-flatness condition, where each particle is at a different elevation, occurs in part, because of uneven metal deposition rates that occur over the surface of the drum at all the different island locations during the process of building-up the height of each island. Also, a random uneven particle deposition occurs over time when particles come out of solution and are deposited in the final portion of the island build-up. The presentation of the individual particles to the raised island area is completely random. Some particles will fall deep into the “log pile” mesh, and others will land on the top curved surface of an individual cylindrical mesh fiber. Some of the abrasive particles will come to rest on other particles that have already been plated onto the mesh, forming standing “rock towers” of particles. Further, the plating process creates nominal island height differences that vary from island to island, in part, due to the different characteristics of the individual fibers of the mesh cloth. The height thickness of each island, as measured from the surface of the plated abrasive particles to the backside of the mesh cloth, or to the island bottom, is not precisely uniform. Another thickness tolerance disadvantage of this product occurs when the plated cloth material is stripped from the electrically conductive metal base and attached with adhesive to a backing substrate sheet to form a laminated abrasive article. This laminated abrasive article does not have precise overall thickness control due to thickness variations in the island plated cloth material, in the backing sheet, and due to thickness variations in the laminating adhesive layer. There is no possible height control mechanism that can be employed to assure that there exists a uniform flat level surface of the individual diamond abrasive particles over the complete surface area of the abrasive article. Diamonds that are bonded at different elevations below the uppermost surface of the top surface of the fiber “logs” in the “log jam” that forms the foundation of the raised island structures are not used and are wasted. Further, there is no control over the thickness variation of the woven mesh material and no description of techniques to level-smooth it down to the surface of the photo resist covered electrical conducting plate used as a geometric reference base for the plating process. After sufficient plating has been achieved, the electrically insulated cloth, made of plastic fibers, is stripped away from the photoresist plate, which can be used again with another mesh cloth. The cloth can then be attached to a backing material or it can be dissolved away with strong chemicals or acids. Attaching the plated cloth with PSA (pressure sensitive adhesive) to a backing introduces new variance in the total thickness of the abrasive article. This process can be used to produce a rectangular sheet, but when a circular disk is punched out with the use of a punch-and-die set, the round surface of the die set will intersect with small portions of the typical round islands and either remove a sliver from some islands, or, leave just a sliver of a rather tall island weakly attached to the backing. In either case, the shearing action of a die punch will tend to jam the sliver portion of the island into the matching die set members. This jamming action will introduce unbalanced forces that will tend to push the island, or a crescent shaped sliver of an island sideways, which will weaken the islands structural attachment to the disk backing. Then the problem of “edge shelling” described earlier occurs and these raised island edge-slivers, or whole island structures, will tend to break loose during grinding and cause scratches that will occur on a lapped workpiece surface. Flex-Diamond® electroplated type of raised island diamond abrasive article sheets available from the 3M Company, St Paul, Minn. have been used to flat-grind workpiece surfaces at high rotational surface speeds using 12 inch (30.5 cm) diameter abrasive disks and these disks have successfully produced workpiece surfaces that had a very precise flatness. There was no indication of the occurrence of hydroplaning of the workpiece using the electroplated raised island product at rotational speed of up to 3,000 RPM. However, these precisely flat workpiece surfaces were simultaneously not polished smooth by the rotating disk abrading action, where the smoothness is relative to the micron size rating of the abrasive particle size of the abrasive article. After the workpiece surfaces were ground flat with the metal plated raised-island abrasive article the surface of the workpiece was so rough that it was not possible to establish the flatness of the ground surface by the use of an optical flat lens test system that allows the visual observation of fringe lightbands. Instead, many measurements (typically hundreds) were made on the workpiece surface by use of a coordinate measuring machine having a 0.0001 inch (2.54 micrometer) measurement readout capability and a theoretical plane of the ground surface was formed by regression analysis using the X, Y and Z coordinate measurements at the many test points of the workpiece surface. Then plots were made of the different areas of the error deviation of the localized non-flat areas of the workpiece surface area from the elevation of the theoretical calculated plane. These error plots gave an accurate description of the out-of-flat areas of the workpiece surface including both the magnitude of the errors and the location of the saddle, and other, shapes that were ground into the workpiece surface. Flat surfaced (non-island) abrasive disk articles of the same 12 inch (30.5 cm) diameter size having the same abrasive particle size rating tended to produce polished workpiece surface that were much smoother than was produced by the electroplated raised island articles under the same rotational speed conditions but these smooth surfaces were not precisely flat. This plated raised island product cannot be used to produce both a precisely smooth and flat workpiece surface, primarily because of the non-uniformity of the elevation of individual abrasive particles that are electroplate bonded to the irregular shaped raised island structures prevent the generation of a smooth surface. A woven mesh fiber cloth is used to produce the metal plated abrasive coated islands as this cloth can be easily stripped away from the island-patterned photo resist backing plate after the islands are formed on, and through the thickness, of the cloth during the island-forming electro plating process. Direct plating of abrasive particles to the top surface of island structures is described by Gorsuch but is not used as it is too difficult to separate the direct plated island from the electrically exposed areas of the photo resist plate. There is no discussion of the concerns of hydroplaning of the workpiece when used at the high speeds desired for abrading with diamond abrasive, which the height of the raised islands easily prevents. Instead, there is only discussion of a passageway for the water to travel outward to flush out the swarf generated as grinding particles are removed from the workpiece surface. Gorsuch makes an attempt to produce a flat level diamond abrasive surface, indicating he is aware of only the fundamental problem with this invention. He first plates a thin layer of metal in an array of islands “upside down” on a smooth cylinder. Then he plates on a layer of diamonds, which is followed by adding a cloth mesh and then adds a layer of metal plating on top of the diamonds which are now fully encapsulated into the thick layer of plated metal. The mesh is stripped off the drum to use the diamonds that originally lay on the flat surface of the drum. However, all the diamonds are completely buried in the plated metal and are useless for use as an abrasive article. Further, there was no description of uncurling a sheet of this material from the curvature of the drum and laying it flat for use as a disk without bending or distorting the abrasive metal plated sheet. The top surface of the raised island is formed in a non-flat cylindrical shape that matches the cylindrical curvature of the surface of the plating drum. Another part of the invention produces a disk with islands of abrasive. These are very thick disks that have a pattern of islands, which are raised 25 percent to 50 percent (of the overall thickness of the disk) above the disk base or backing. A thick layer of abrasive slurry of abrasive particles mixed in a resin is deposited on a backing and the thickness is controlled by the use of mold plates. No description is made of how critical it is to control the flatness of the upper surface of the molded layer of abrasive, or of how the abrasive surface is maintained flat during wear. Further, no description was made of any of the issues of hydroplaning at high speed with water lubricants which is a primary concern for use with high speed lapping. A description is given of the use of very large hemispherical elements of metal that have a diameter of 0.5 to 3 mm which has generally only five abrasive particles which have a very large average size of 250 micrometer diameter. These abrasive particles are located at the top and along the lower side-walls of each hemisphere and are metal plated to be embedded from 30 percent to 50 percent as an integral part of the metal hemisphere. These hemispheres are high enough to act as islands and the rounded tops would also aid in preventing hydroplaning at high speeds. However, this type of construction with very tall domes having only a single abrasive particle located on the very apex of the dome peak has little use for lapping. The single particle will be very aggressive in material removal but it will only produce distinct scratches as it removes a single track of material as it passes over a workpiece surface. This highest particle will have to become worn down along with some of the parent metal used for the dome construction before another particle will be active in partnership with the first. Having only five particles on a huge dome means most of the whole dome must effectively be worn down before the lower particles are engaged as grinding elements. The whole abrasive grinding load forces are so concentrated on single grains of abrasive that the grains tend to be knocked out of place, or “pulled” from the very strong plated metal binding. Use of expensive abrasive particles such as diamond seems totally out of place economically for this type of abrasive article construction. It has absolutely no value for lapping. None of the plating methods employed in this plating technique of forming abrasive articles has any capability of controlling the height of the particles relative to the backside of a backing, which is a critical factor for lapping at high surface speeds. FIG. 6 (Prior Art) is a cross section view of abrasive particle coated plated metal islands as described by Gorsuch. Island structures 68 are formed by metal plating geometric patterns on a cloth material 60 and abrasive particles 64 are fixtured to the surface of the metal islands 68 by a build-up of plated metal around each individual abrasive particle 64. Abrasive particles 62 also exist in the valleys or recessed areas between the island structures 68. There is no reference to controlling the variation in height 66 between islands or in controlling the height 70 of each individual islands as measured between the top surface of the islands 68 and the backside of the backing 60. In U.S. Pat. No. 5,318,604, Gorsuch forms plated abrasive particle covered elements where a metal element structure is first formed. This structure then has abrasive particles attached to the element top surface by further depositing plated metal on the element as abrasive particles are deposited on the metal structure. Many of these elements are formed through a cloth material, the cloth is removed from a plating tank grounding plate surface and the cloth is dissolved away to leave many of the individual small abrasive elements. The abrasive elements are then mixed with a polymer resin and the abrasive-resin mixture is then molded onto the surface of a disk backing sheet to form a geometric pattern of raised abrasive-polymer islands that are attached to the backing disk. FIG. 7 (Prior Art) is a cross section view of metal plated abrasive elements. An abrasive element 80 has a metal plated element structure 84 that has abrasive particles 82 metal bonded to the top surface of the structures 84. FIG. 8 (Prior Art) is a cross section view of raised island structures that are attached to a backing sheet. A backing sheet 90 has raised island structures 88 that are mold-formed from a mixture of a polymer 87 and abrasive coated plated metal structure elements 86 and there are with recessed valleys or channels 85 between the islands 88. FIG. 9 (Prior Art) is a top view of an abrasive disk article having molded abrasive raised islands. The abrasive disk 92 has a backing 93 that has attached abrasive mixture molded islands 96 that have recessed channel valley areas 95 that are located between the islands 96. There is a gap between the edges of all the islands 96 and the outer periphery of the disk 92 as shown by the recessed area gap width 94.
U.S. Pat. No. 4,315,720 (Ueda et al.) describes the use of a rotary wheel to produce spherical droplets of metal or slag where a melt material is feed into the wheel center and splits into small diameter linear streams. The spherical droplets that are formed from the streams become solidified and have a diameter larger than the stream diameter.
U.S. Pat. No. 4,272,926 (Tamulevich) describes the use of a abrasive coated sheet to polish the face end of a fiber optic connector where the fiber optic is positioned precisely perpendicular to the abrasive sheet mounted on a flat platen and the connector is moved relative to the sheet to produce a precisely flat and smooth facet. This same type of abrading process may be used to polish other components used with fiber optic systems.
U.S. Pat. No. 4,314,827 (Leitheiser, et al.) discloses processes and materials used to manufacture sintered aluminum oxide-based abrasive material having shapes including spherical shapes that are processed in an angled rotating kiln at temperatures up to 1350 degrees C. with a final high temperature zone residence time of about 1 minute.
U.S. Pat. No. 4,341,439 (Hodge) describes the use of abrasive to polish the face end of a fiber optic connector to produce a precisely flat and smooth face on the fibers.
U.S. Pat. No. 4,364,746 (Bitzer, et al.) discloses the use of composite abrasive agglomerates. Agglomerates include spherical abrasive elements. Composite agglomerates are formed by a variety of methods. Individual abrasive grains are coated with various materials including a silica ceramic that is applied by melting or sintering. Agglomerated abrasive grains are produced by processes including a fluidized spray granulator or a spray dryer or by agglomeration of an aqueous suspension or dispersion. Composite agglomerates contain between 10 and 1000 abrasive fine P 180 grade abrasive particles and agglomerates contain between 2 and 20 abrasive particles for P 36 grade abrasive.
U.S. Pat. No. 4,373,672 (Morishita, et al.) discloses a high speed air-bearing electrostatic automobile body sprayer article that produces 15 micron to 20 micron paint-drop particles by introducing a stream of a paint liquid into a segmented bore opening rotating head operating at 80,000 rpm. Comparatively, a slower like-sized ball-bearing sprayer head rotating at 20,000 rpm produces 55 micron to 65-micron diameter drops. A graph showing the relationship between the size of paint drop particles and the rotating speed of the spray head is presented. The 20 micron paint drops ejected from the sprayer head travel for some time over a distance before contacting an automotive body, during which time surface tension forces will act on the individual drops to form the drops into spherical shapes.
U.S. Pat. No. 4,421,562 (Sands) discloses microspheres formed by spraying an aqueous sodium silicate and polysalt solution with an atomizer wheel.
U.S. Pat. No. 4,426,484 (Saeki) describes phenolic resins which have the cure time accelerated by using special additives.
U.S. Pat. No. 4,541,566 (Kijima, et al.) discloses use of tapered wall pins in a centrifugal rotating head spray dryer that produces uniform 50 to 100 micron sized atomized particles using 1.0 to 4.0 specific gravity, 5 to 18,000 c.p. viscosity feed liquid when operating at 13 to 320 m/sec rotating head peripheral velocity.
U.S. Pat. No. 4,541,842 (Rostoker) discloses spherical agglomerates of encapsulated abrasive particles including 3 micron silicone carbide particles or cubic boron nitride (CBN) abrasive particles encapsulated in a porous ceramic foam bubble network having a thin-walled glass envelope. The composites are formed into spherical shapes by blending and mixing an aqueous mixture of ingredients including metal oxides, water, appropriate abrasive grits and conventional known compositions which produce spherical pellet shapes that are fired. Composite agglomerates of 250-micron size are dried and then fired at temperatures of up to 900 degrees C. or higher using a rotary kiln. Heating of the agglomerates to a temperature sufficiently high to form a glassy exterior shell surface on the agglomerates is done in a reducing atmosphere over a time period short enough to prevent thermal degradation of the abrasive particles contained within the spherical agglomerate. A vertical-shaft furnace is used to produce agglomerates as small as 20 microns.
U.S. Pat. No. 4,586,292 (Carroll et al.) describes an apparatus that provides a complex rotary motion used to lap polish the inside diameter of a spherical surface workpiece.
U.S. Pat. No. 4,652,275 (Bloecher) describes the use of erodible agglomerates of abrasive particles used for coated abrasive articles. The matrix material, joined together with the abrasive particles, erodes away during grinding which allows sloughing off of spent abrasive particles and the exposure of new abrasive grains. The matrix material is generally a wood product such as wood flour selected from pulp. A binder can include a variety of materials including phenolics. It is important that the binder not soften due to heat generated by grinding action. Instead, it should be brittle so as to breakaway. If too much binder is used, the agglomerate will not erode and if too little is used, the mixture of the matrix and the abrasive particles are hard to mix. The preferred agglomerate is made by coating a layer of the mixture, curing it, breaking it into pieces and separating the agglomerate particles by size for coating use. Agglomerates of a uniform size can be made in a pelletizer by spraying or dropping resin into a mill containing the abrasive mineral/matrix mixture. Agglomerates are typically irregular in shape, but they can be formed into spheres, spheroids, ellipsoids, pellets, rods and other conventional shapes. Other methods of making agglomerates include the creation of hollow shells of abrasive particles where the shell breaks down with grinding use to continually expose new abrasive particles. Other solid agglomerates of abrasive particles are mixed with an inorganic, brittle cryolite matrix. A description is made of conventional coated abrasives which typically consist of a single layer of abrasive grain adhered to a backing. It has been found that only up to 15 percent of the grains in the layer are actually utilized in removing any of the workpiece. It follows then that about 85 percent of the grains in the layer are wasted. The agglomerates described here preferably range from 150 micrometers to 3000 micrometers and have between 10 and 1000 individual abrasive grain particles for P180 grains and only 2 to 20 grains of larger P36 grains. These agglomerates far exceed the size required for high speed lapping. In fact, only single layers of diamond particles is required or typically used as a coating for most lapping abrasive articles, so these huge agglomerates have little or no use in lapping. Further, there would not be an effective method of maintaining a flat abrasive surface as the abrasive agglomerates are worn down by abrasive lapping or grinding action.
U.S. Pat. No. 4,710,406 (Fugier) describes a production method for the manufacture of a condensation reaction phenolic resin with different alkali catalysts and which can be diluted up to 1,000 percent.
U.S. Pat. No. 4,773,920 (Chasman et al.) herein incorporated by reference, describes an abrasive sheet article used for abrasive lapping where the backing sheet is less than 0.010 inches (254 micrometers) thick and is preferred to be 0.002 to 0.003 inches (51 to 76 micrometers) thick. Chemical treatments of the backing and mechanical roughing of the backing sheet is described that is used to promote the adhesion between the backing and the abrasive particle binder.
U.S. Pat. No. 4,776,862 (Wiand) discloses diamond and cubic boron nitride abrasive particle surface metallization with various metals and also the formation of carbides on the surface of diamond particles to enhance the bonding adhesion of the particles when they are brazed to the surface of a substrate.
U.S. Pat. No. 4,799,939 (Bloecher) describes use of 70 micrometer diameter hollow glass spheres which are mixed with abrasive particles and a binder to form erodible 150 to 3000 micrometer agglomerates which are used for coating in abrasive articles. The hollow glass spheres are strong enough for the mixing operation and for the process used to form the agglomerate particle. However, they are weak enough that they break when used in grinding. Again, as for U.S. Pat. No. 4,652,275, these agglomerates are much too large and inappropriate for use in high speed lapping.
U.S. Pat. No. 4,903,440 (Larson et al.), herein incorporated by reference, describes the use of different reduced-cost drum cured binder abrasive particle adhesives which allow elimination of the use of web festoon ovens which are used because of the long cure times required by conventional phenolic adhesives used for abrasive webs. Typically a pre-coat, a make coat, having loose abrasive particles imbedded into the make coat and then a size coat are applied to a continuous web backing. No reference is given to processing individual abrasive articles such as abrasive disks. Rather, a continuous backing web is coated with binders and abrasive particles, the binders are cured and then the web is converted into abrasive products such as disks or belts. Resole phenolic resins which are somewhat sensitive to water lubricants are catalyzed by alkaline catalysts and novolac phenolic resins having a source of formaldehyde to effect the cure are described. Viscosity of some binders are reduced by solvents. Fillers include calcium carbonate, calcium oxide, calcium metasilicate, aluminum sulfate, alumina trihydrate, cryolite, magnesia, kaolin, quartz and glass. Grinding aid fillers include cryolite, potassium fluroborate, feldspar and sulfur. Super size coats can use zinc stearate to prevent abrasive loading or grinding aids to enhance abrading. Coating techniques include two basic methods. The first is to provide a pre-size coat, a make coat, the initial anchoring of loose abrasive grain particles and a size coat for tenaciously holding abrasive grains to the backing. The second coating technique is to use a single-coat binder where a single-coat takes the place of the make coat/size coat combination. An ethyl cellosolve and water solvent is referenced for use with a resole phenolic resin.
U.S. Pat. No. 4,918,874 (Tiefenbach) discloses a slurry mixture including 8 micron and less diamond and other abrasive particles, silica particles, glass-formers, alumina, a flux and water, drying the mixture with a 400 degree C. spray dryer to form porous greenware spherical agglomerates that are sintered. Fluxes include an alkali metal oxide, such as potassium oxide or sodium oxide, but other metal oxides, such as, for example, magnesium oxide, calcium oxide, iron oxide, etc., can also be used.
U.S. Pat. No. 4,930,266 (Calhoun, et al.) discloses the application of spherical abrasive composite agglomerates made up of fine abrasive particles in a binder in controlled dot patterns where preferably one abrasive agglomerate is deposited per target dot by use of a commercially available printing plate. Small dots of silicone rubber are created by exposing light through a half-tone screen to a photosensitive silicone rubber material coated on an aluminum sheet and the unexposed rubber is brushed off leaving small islands of silicone rubber on the aluminum. The printing plate is moved through a mechanical vibrated fluidized bed of abrasive agglomerates that are attracted to and weakly bound to the silicone rubber islands only. The plate is brought into nip-roll pressure contact with a web backing which is uniformly coated by a binder resin which was softened into a tacky state by heat thereby transferring each abrasive agglomerate particle to the web backing. Additional heat is applied to melt the binder adhesive forming a meniscus around each particle, which increases the bond strength between the particle and the backing. The resulting abrasive article has gap-spaced dots of abrasive agglomerate particles on the backing but the agglomerates are attached directly to the backing surface and are not raised away from the backing surface. Each composite abrasive agglomerate bead is preferably a spherical composite of a large number of abrasive grains in a binder; the agglomerates typically range in size from 25 to 100 microns and contain 4-micron abrasive particles. It is indicated that the composite abrasive agglomerate granules should be of substantially equal size, i.e., the average dimension of 90% of the composite granules should differ by less than 2:1. Abrasive grains having an average dimension of about 4 microns can be bonded together to form composite sphere granules of virtually identical diameters, preferably within a range of 25 to 100 microns. Preferably, the abrasive composite granules have equal sized diameters where substantially every granule is within 10% of the arithmetic mean diameter so that the granules protrude from the surface of the binder layer to substantially the same extent and also so the granules can be force-loaded equally upon contacting a workpiece. Granules are spherical in shape or have a shape that has approximately that same thickness in every direction. By individually positioning the equal sized granules to be spaced equally from adjacent granules, the granules each bear the same load and hence wear at substantially identical rates and tend to be equally effective. Consequently, workpieces continue to be polished uniformly. One difficulty with this abrasive product, even with abrasive composites having uniform diameters where each composite granule can be positioned to protrude to the same extent from the binder layer, the variation in the thickness in the backing thickness is not considered. If there are significant variations in the backing thickness, even equal sized individual composite abrasive agglomerates coated on a abrasive article rotating at high lapping surface speeds of 8,000 surface feet per minute will not evenly contact a workpiece surface. Eventually, the highest positioned composite abrasives will wear down and adjacent composite agglomerates will be contacted by the workpiece surface. It is necessary to control the diameter of the composite agglomerates, the thickness variation of the binder and the variation of the coated surface height of the backing, relative to the back platen mounting side of the backing, to some fraction of the diameter of the average diameter of the abrasive composites to attain effective utilization of all or most of the abrasive composite agglomerates.
U.S. Pat. No. 4,931,414 (Wood, et al.) discloses the formation of microspheres by forming a sol-gel where a colloidal dispersion, sol, aquasol or hydrosol of a metal oxide (or precursor thereof) is converted to a gel and added to a peanut oil dehydrating liquid to form stable spheriods that are fired. A layer of metal (e.g. aluminum) can be vapor-deposited on the surface of the microspheres. Various microsphere-coloring agents were disclosed.
U.S. Pat. No. 4,974,373 (Kawashima, et al.) discloses a lapping abrasive tool having a adhesive bonded layer of abrasive particles where he describes the desirability of having a single layer of abrasive particles on the surface of the tool for lapping of workpieces. He discloses where multiple layers of abrasive particles in particle agglomerates can scratch the surface of a workpiece.
U.S. Pat. No. 5,015,266 (Yamamoto) describes surface-textured abrasive articles that have an abrasive coating applied to roll formed embossed backing sheets where the abrasive coating follows the contours of the embossed patterns.
U.S. Pat. No. 5,090,968 (Pellow) describes the formation of abrasive filaments by forcing a gelled hydrated mixture of a metal oxide into a moving porous belt to produce abrasive precursor filaments of substantially constant length. The filaments are treated to make them non-sticky as they are still attached to the belt after which they are removed from the belt and fired at a high temperature to convert them into filament abrasive particles. It is not possible to make spherical abrasive particles by this process.
U.S. Pat. No. 5,108,463 (Buchanan) describes carbon black aggregates incorporated into a super size coat which also included kaolin.
U.S. Pat. No. 5,110,659 (Yamakawa, et al.) discloses an abrasive lapping tape having very small abrasive particles where the tape has a defined smooth surface. He describes the undesirability of other abrasive particle coated lapping tapes that have agglomerations of fine abrasive particles that produce scratches in the surface of workpieces that include magnetic heads.
U.S. Pat. No. 5,137,542 (Buchanan) describes a coated abrasive article which has a coated layer of conductive ink applied to the surface of the article, either as a continuous film or the back side of the backing or as printed “island” patterns on the abrasive particle size of the article to prevent the buildup of static electricity during use. Static shock can cause operator injury or ignite wood dust particles. The islands coated on 3M Company Imperial® abrasive were typically quite large 1 inch (2.54 cm) diameter dots and cover only about 22 percent of the article surface. Further, they are very thin, about 4 to 10 micrometers. No reference is made to the affect of the raised islands on hydroplaning effects when used with a water lubricant and no reference is made to high speed lapping. Raised islands of this height would provide little, if any, benefit for hydroplaning. Further, islands of this large diameter would also develop a significant boundary layer across its surface length. Also, top coatings such as these electrically conductive particle filled materials would not allow the typically small mono layers of diamonds used in lapping films to abrasively contact the workpiece surface until the static coating was worn away, after which time it is no longer effective in static charge build-up prevention. Description is made of using polyester film as a backing material for lapping abrasive articles. Bond systems include phenolic resins and solvents include 2-butoxyethanol, toluene, isopropanol, or n-propyl acetate. Coating methods include letterpress printing, lithographic printing, gravure printing and screen printing. For gravure printing, a master tool or roll is engraved with minute wells which are filled with coatable electrically conductive ink with the excess coating fluid removed by a doctor blade. This coating fluid is then transferred to the abrasive article.
U.S. Pat. No. 5,175,133 (Smith, et al.) discloses bauxite (hydrous aluminum oxide) ceramic microspheres produced from a aqueous mixture with a spray dryer manufactured by the Niro company or by the Bowen-Stork company to produce polycrystalline bauxite microspheres. Gas suspension calciners featuring a residence time in the calcination zone estimated between one quarter to one half second where microspheres are transported by a moving stream of gas in a high volume continuous calcination process. Scanning electron microscope micrograph images of samples of the microspheres show sphericity for the full range of microspheres. The images also show a wide microsphere size range for each sample, where the largest spheres are approximately six times the size of the smallest spheres in a sample.
U.S. Pat. No. 5,190,568 (Tselesin) discloses a variety of sinusoidal and other shaped peak and valley shaped carriers that are surface coated with diamond particles to provide passageways for the removal of grinding debris. There are a number of problems inherent with this technique of forming undulating row shapes having wavelike curves that are surface coated with abrasive particles on the changing curvature of the rows. The row peaks appear to have a very substantial heights relative to the size of the particles which indicates that only a very small percentage of the particles are in simultaneous contact with a workpiece surface. One is the change in the localized grinding pressure imposed on individual particles, in newtons per square centimeter, during the abrading wear down of the rows. At first, the unit particle pressure is highest when a workpiece first contacts only the few abrasive particles located on the top narrow surface of the row peaks. There is a greatly reduced particle unit pressure when the row peaks are worn down and substantially more abrasive particles located on the more gently sloped side walls are in contact with the workpiece. The inherent bonding weakness of abrasive particles attached to the sloping sidewalls is disclosed as is the intention for some of the lower abrasive particles, located away from the peaks, being used to structurally support the naturally weakly bonded upper particles. The material used to form the peaks is weaker or more erodible than the abrasive particles, which allows the erodible peaks to wear down, expose, and bring the work piece into contact with new abrasive particles. Uneven wear-down of the abrasive article will reduce its capability to produce precise flat surfaces on the work piece. Abrasive articles with these patterns of shallow sinusoidal shaped rounded island-like foundation ridge shapes where the ridges are formed of filler materials, with abrasive particles coated conformably to both the ridge peaks and valleys alike is described. However, the shallow ridge valleys are not necessarily oriented to provide radial direction water conduits for flushing grinding debris away from the work piece surface on a circular disk article even prior to wear-down of the ridges. Also, a substantial portion of the abrasive particles residing on the ridge valley floors remain unused as it is not practical to wear away the full height of the rounded ridges to contact these lower elevation particles.
U.S. Pat. No. 5,199,227 (Ohishi) describes raised island structure protuberances that are coated with abrasive particles. FIG. 22 (Prior Art) is a cross section view of the Ohishi abrasive coated raised island structures. The protuberances 246 that are attached to a backing sheet 250 are coated with abrasive particles 244. There is no description of precisely controlling the height of the abrasive 244 from the backside of the backing 250 as indicated by the thickness or height dimension 248. The cavities that may be formed into the surface of the belt may be open cells that extend through the thickness of the flexible belt or cavity sheet.
U.S. Pat. No. 5,201,916 (Berg et al), herein incorporated by reference, describes abrasive particles that are formed with the use of a cavity cell belt or sheet that has a planar surface. A dispersion mixture of particles that can be converted into a metal oxide abrasive particle is formed as a liquid that is introduced into the belt cavity cells. The cells are filled with the liquid mixture dispersion flush with the flat top surface of the belt. The liquid can be gelled into a three dimensional network of solids dispersed in a liquid where the gel will not flow from an inverted test tube. The dispersion or mixture can be gelled before it is introduced into the belt cavities to fill them. Also, a peptizing agent may be added to the dispersion mixture to produce a more stable hydrosol or colloidal dispersion. Then a portion of the liquid in the dispersion mixture is removed while the mixture resides in the individual belt cavities whereby the precursor abrasive particles that are formed by the shape of each belt cavity shrinks in size while retaining the basic shape of the cavity. The preferred shape of a cavity is a flat-topped triangular shape so the formed abrasive particles in these cavities also have a flat-topped triangular shape. Each shrunken abrasive triangle abrasive precursor is reduced in size enough during the shrinkage that they then fall out of the cavities as solidified particles after shrinking due to gravity. The shrunken volume of the precursor of the abrasive particle can be 80% or less than the volume of the original liquid dispersion mixture that was initially deposited in the mold cavity. Care is exercised to not overheat the mixture during shrinkage to prevent cracks in the body of the solidified precursor particles. Typically 40% of the liquid is removed from the dispersion in the step in the process of forming the solidified abrasive particle precursor. The solidified particles are then collected to be subjected to heating to calcine the particles where all the volatile material is removed. Further heating then sinters or fires the calcined abrasive precursor particles into a hardened metal oxide ceramic abrasive particle. All of the finished abrasive particle shapes have flat and parallel front and back sides as they are formed by a speed controlled rubber squeegee to fully fill the flat planar cavity belt with the liquid mixture. The viscous liquid mixture contained in each individual cavity initially takes the geometric shape of the belt cavity shape to form the flat topped mixture geometric shapes. The cavity belt may be coated with a mold release agent prior to introduction of the dispersion into the cavity cells. As the cavity cell mixture particles are dried and shrunk into solid geometric forms prior to their being ejected by gravity from the belt it is not possible to produce a spherical abrasive particle shape by this process. Here, there is no provision made for surface tension forces to act on the individual abrasive particle lumps while the particle lump entities are in a fully free flowing liquid state and as the lump is in an unconstrained free state of suspension. There is no discussion by Berg of adding abrasive particles, including diamond particles, to the mixture prior to the mixture being introduced into the belt cavities. The high firing temperatures that are disclosed, which the metal oxide precursor particles are subjected to, would tend to destroy any diamond particles that were encapsulated in the form shaped abrasive particles. The metal oxide abrasive particles are then coated with a conventional resole phenolic resin on a backing sheet and cured in an oven to produce an abrasive article.
FIG. 29A (Prior Art) is a cross section view of the Berg triangular shaped abrasive particles and particle forming belt. The particle forming belt 335 has belt wall sections 331 that form cavity openings that are filled to the flat belt surfaces with a gelled mixture of suspended metal or other oxide particles in a water based solution to form a liquid flat sided triangular mixture lump 337 that shrinks to a smaller sized solidified flat sided triangular lump 333 which falls away from the belt 335. Two solidified falling abrasive flat sided triangular shaped lumps 339 are then collected and subjected to heating and firing to convert the abrasive lumps into hardened abrasive flat sided triangular shaped particles.
U.S. Pat. No. 5,221,291 (Imatani) describes the use of a polyimide resin for the combination use as an adhesive bonding agent for abrasive particles, and also, to form an abrasive sheet. Diamond particles were dispersed in solvent thinned polyimide resin and coated on a flat surface with 60 micrometer diamond particles to form an abrasive sheet where 20% of the sheet material is made up of abrasive particles. The sheet was tested at very low speeds of 60 rpm and did abrasively remove workpiece material, leaving a smooth workpiece surface. However, the abrasive particles are principally buried within the thickness of the resin mixture sheet as the abrasive and resin mixture forms the thin abrasive disk sheet article. Much of the expensive diamond particles are located at the bottom layer of the abrading sheet structure and so are not available for use as grinding agents but the polyimide successfully bonds the diamonds within the sheet.
U.S. Pat. No. 5,232,470 (Wiand) discloses raised molded protrusions of circular shapes composed of abrasive particles mixed in a thermoplastic binder attached to a circular sheet of backing.
U.S. Pat. No. 5,251,802 (Bruxvoort, et al.) discloses the use of solder or brazing alloys to bond diamond and other abrasive particles to a flexible metal or non-metal backing material.
U.S. Pat. No. 5,273,805 (Calhoun, et al.) discloses the use of a silicone material to transfer abrasive particles in patterns onto a tacky adhesive coated backing.
U.S. Pat. No. 5,304,225 (Gardziella) describes phenolic resins which typically have high viscosity which can be lowered by the addition of solvents or oils.
U.S. Pat. No. 5,368,618 (Masmar) describes preparing an abrasive article in which multiple layers of abrasive particles, or grains, are minimized. Some conventional articles have as many as seven layers of particles which is grossly excessive for lapping abrasive media. He describes “partially cured” resins in which the resin has begun to polymerize but which continues to be partially soluble in an appropriate solvent. Likewise, “fully cured” means the resin is polymerized in a solid state and is not soluble. If the viscosity of the make coat is too low, it wicks up by capillary action around and above the individual abrasive grains such that the grains are disposed below the surface of the make coat and no grains appear exposed. Phenolic resins are cured from 50 degrees to 150 degrees C. for 30 minutes to 12 hours. Fillers including cryolite, kaolin, quartz, and glass are used. Organic solvents are added to reduce viscosity. Typically 72 to 74 percent solids are used for resole phenolic resin binders. Special tests demonstrate that a partially cured resin is capable of attaching loose abrasive mineral grains which are drop coated onto test slides with the result that higher degree of cure results in lower mineral pickup and lower degree of cure results in less mineral pickup. Abrasive grains can be electrostatically projected into the make coat where the ends of each grain penetrates some distance into the depth of the make coat. No description was provided about the desirability, necessity, or ability of the grain application process having a flat uniform depth of the tops of each particle for high speed lapping.
U.S. Pat. No. 5,397,369 (Ohishi) describes phenolic resins used in abrasive production which have excessive viscosity where a large amount of solvent is required for dilution to adjust the viscosity within an appropriate range. Examples of organic solvents with high boiling points include cyclohexanone, and cyclohexanol. Solvents having an excessively high boiling point tend to remain in the adhesive binder and results in insufficient drying. When the boiling point of a solvent is too low, the solvent leaves the binder too fast and can result in defects in the abrasive coating, sometimes in the form of foamed areas. Additives such as calcium carbonate, silicone oxide, talc, etc. fillers, cryolite, potassium borofluoride, etc. grinding aids and pigment, dye, etc. colorants can be added to the second phenolic adhesive (size coat) used in the abrasive manufacture.
U.S. Pat. No. 5,489,204 (Conwell, et al.) discloses a non rotating kiln apparatus useful for sintering previously prepared unsintered sol gel derived abrasive grain precursor to provide sintered abrasive grain particles ranging in size from 10 to 40 microns. Dried material is first calcined where all of the mixture volatiles and organic additives are removed from the precursor. The stationary kiln system described sinters the particles without the problems common with a rotary kiln including loosing small abrasive particles in the kiln exhaust system and the deposition on, and ultimately bonding of abrasive particles to, the kiln walls. A pusher plate advances a level mound charge quanity of unsintered abrasive grains dropped within the heated body of a fixed position kiln having a flat floor to sinter dried or calcined abrasive grains. The depth of the level mound of unsintered particles is minimized to a shallow bed height to aid in providing consistent heat transfer to individual unsintered abrasive precursor grains, and in consistently providing uniformly sintered abrasive grains. The abrasive grain precursor remains in the sintering chamber for a sufficient time to fully sinter the complete body volume of each individual particle contained in the level mound bed. The surface of each unsintered particle is heated to the temperature of the sintering apparatus in less than a 1-second time period.
U.S. Pat. No. 5,496,386 (Broberg, et al.) discloses the application of a mixture of diluent particles and also shaped abrasive particles onto a make coat of resin where the function of the diluent particles is to provide structural support for the shaped abrasive particles.
U.S. Pat. No. 5,549,961 (Haas, et al.) discloses abrasive particle composite agglomerates in the shape of pyramids and truncated pyramids that are formed into various shapes and sintered at high temperature. Numerous references are made to the deployment of individual abrasive microfinishing beads on a backing but no reference is made concerning the production of these spherical beads by the technology disclosed in this patent. Rather, the creation of composite agglomerates is focused on the production of pyramid shaped agglomerates. The breakdown of abrasive composite agglomerates is characterized in the exposed surface regions of the abrasive composite where small chunks of abrasive particles and neighboring binder material are loosened and liberated from the working surfaces of the abrasive composite, and new or fresh abrasive particles are exposed. This breakdown process continues during polishing at the newly exposed regions of the abrasive composites. During use of the abrasive article of this invention, the abrasive composite erodes gradually where worn abrasive particles are expelled at a rate sufficient to expose new abrasive particles and prevent the loose abrasive particles from creating deep and wild scratches on or gouging a workpiece surface. The composite abrasive particles including diamond contained in the agglomerates range in size from 0.1 to 500 microns but preferably, the abrasive particles have a size from 0.1 to 5 microns.
U.S. Pat. No. 5,549,962 (Holms) describes the use of pyramid shaped abrasive particles by use of a production tool having three-dimensional pyramid shapes generated over its surface which are filled with abrasive particles mixed in a binder. This abrasive slurry is introduced into the pyramid cavity wells and partially cured within the cavity to sufficiently take on the shape of the cavity geometry. Then the pyramids are either removed from the rotating drum production tool for subsequent coating on a backing to produce abrasive articles, or, a web backing is brought into running contact with the drum to attach the pyramids directly to the backing to form an abrasive web article. If a web backing is used is contact with the drum, the apexes of the pyramids are directed away from the backing. If loose discrete pyramids are produced by the drum system, the pyramids can be oriented on a backing with the possibility of having the pyramid apex up, or down or sideways relative to the backing. The pyramid wells may be incorporated into a belt and also, these forms can extend through the thickness of the belt to aid in separating the abrasive pyramid particles from the belt.
Over time, many attempts have been made to distribute abrasive grits or particles on the backing in such a method that a higher percentage of the abrasive grits or particles can be used. Merely depositing a thick layer of abrasive grits or particles on the backing will not solve the problem, because grits or particles lying below the topmost grits or particles are not likely to be used. The use of agglomerates having random shapes where abrasive particles are bound together by means of a binder are difficult to predictably control the quantity of abrasive grits or particles that come into contact with the surface of a workpiece. For this reason, the precisely shaped (pyramid) abrasive agglomerates are prepared. Some pyramid-shaped particles are formed which do not contain any abrasive particles and these are used as dilutants to act as spacers between the pyramid abrasive agglomerates when coated by conventional means. Many different fillers and additives can be used including talc and montmorillonite clays. Care is exercised to provide sufficient curing of the agglomerate binders in the drum cavities so that the geometry of the cavity is replicated. Generally, this requires a fairly slow rotation of the production tooling cavity drum. No description is given to the accuracy of the height or thickness control of the resultant abrasive article which incorporates these very large agglomerate pyramids which typically are 530 micrometers high and have a 530 micrometer base length. Thickness variations of conventional lapping disk abrasive sheets generally are held within 3 micrometers in order for it to be used successfully. The system of using the large pyramids described here cannot produce an abrasive article of the precise thickness control required for high speed lapping for a number of fundamental reasons. Some of these reasons are listed here. First, creation of many precise sized pyramid cavities by use of a belt that is replicated into a plastic form to control the belt cost adds error due to the sequential steps taken in the replication process. Variations in binder cures from production run to run and also variations in binder cures across the surface of a drum belt result in pyramids that are distorted from the original drum wells. For backing belts to be integrally bonded to the pyramids during the formation of the pyramids, it is required that any adhesive binder used to join the agglomerate be precisely controlled in thickness. Thickness control is difficult to achieve with this type of production equipment as there are many thickness process variables that must be controlled that are in addition to those variables that are controlled to successfully create or form precise shaped pyramids. The backing material must be of a precise thickness. Random orientation of the large agglomerates will inherently produce different heights at the exposed tops of the agglomerates depending on whether an agglomerate has its apex up, it lays sideways, or has its sharp apex embedded in a make coat of binder. The use of pyramids where all the apexes are up and the bases are nested close together produces grinding effects that change drastically from the initial use where only the tips of the pyramids contact the workpiece, to a final situation where the broad bases contact the workpiece when most of the pyramid has worn away. There was no description of the inherent advantage of the use of upright pyramids for hydroplaning or swarf removal which is a natural affect of these relatively tall “mountain pyramids” and the “valleys” between them which can carry off the water quite well. There was no discussion of the use of this pyramid material for high speed lapping or grinding. The water lubricant effects on grinding would change significantly as the abrasive article wears down. There is a fundamental flaw in the design of the pyramid for upright use. Most of the abrasive material contained on the pyramid lies at the base which is worn out last during the phase of wear when the variations in thickness of the backing, and other thickness variation sources, prevent a good proportion of the bases from contacting a workpiece surface. When using these large-sized pyramid agglomerates, they are designed to progressively breakdown and expose new cutting edges as the old worn individual abrasive particles are expended as the support binder is worn down, exposing fresh new sharp abrasive particles. Most of the value of the expensive abrasive particles lies in the base, as most of the volume of a triangle is in the base. Here, most of the valuable abrasive particles at the base areas will never be used and are wasted. Further, as wear-down of the pyramids is prescribed by selection of the pyramid agglomerate binder, the level surface of the abrasive disk will vary from the inside radius to the outside radius as the contact surface speed with a workpiece will be different due to the radius affect of a rotating abrasive platen. The pyramids are grossly high compared to the size of abrasive particles or abrasive agglomerates and this height results in uneven wear across the surface of an abrasive article that often is far in excess of that allowable for high speed flat lapping. This uneven wear prevents the use of this type of article for high speed lapping. Inexpensive abrasive materials such as aluminum oxide can be used for the pyramid agglomerates but it is totally impractical to use the extra hard, but very expensive, diamond abrasives in these agglomerates. The flaws inherent in the use of conventional pyramid shaped type of agglomerates, due to the size variations in the agglomerates, would tend to prevent them from being used successfully for flat lapping. First, agglomerates can be made and then sorted by size prior to use as a coated abrasive. Also, the configuration of a generally round shaped conventional agglomerate would certainly wear more uniformly than wearing down a pyramid which has a very narrow spiked top and, after wear-down, a base which is probably ten times more large in cross-sectional surface area than the pyramid top. Random orientation of the pyramid shape does not help this geometric artifact. Another issue is the formulation of the binder and filling used in a conventional agglomerate. A wide range of friable materials such as wood products can be joined in a binder which can be selected to produce an agglomerate by many methods, including furnace baking, etc. The binder used in the production of the pyramids must be primarily selected for process compatibility with the fast cure replication of the drum wells and not for consideration of whether this binder will break down at the desired rate to expose new abrasives at the same rate the abrasive particles themselves are wearing down. It does not appear that this pyramid shaped agglomerate particle has much use for high speed lapping. Use of a polyethylene terephthalete polyester film with a acrylic acid prime coat is described.
U.S. Pat. No. 5,551,961 (Engen) describes abrasive articles made with a phenolic resin applied as a make coat used to secure abrasive particles to the backing by applying the particles while the make coat is in an uncured state, and then, the make coat is pre-cured. A size coat is added. Alternatively, a dispersion of abrasive particles in a binder is coated on the backing. The use of solvents is described to reduce the viscosity of the high viscous resins where high viscosity binders cause “flooding”, i.e., excessive filling in between 30 to 50 micrometer abrasive grains. Also, non-homogenous binder resins result in visual defects and performance defects. Both flooding and non-homogenous problems can be reduced by the use of organic solvents which are minimized as much as possible. Resole phenolic resins experience condensation reactions where water is given off during cross linking when cured. These phenolics exhibit excellent toughness, dimensional stability, strength, hardness and heat resistance when cured. Fillers used include calcium sulfate, aluminum sulfate, aluminum trihydrate, cryolite, magnesium, kaolin, quartz and glass and grinding aid fillers include cryolite, potassium fluoroborate, feldspar and sulfur. Abrasive particles include fused alumina zirconia, diamond, silicone carbide, coated silicone carbide, alpha alumina-based ceramic and may be individual abrasive grains or agglomerates of individual abrasive grains. The abrasive grains may be orientated or can be applied to the backing without orientation. The preferred backing film for lapping coated abrasives is polymeric film such as polyester film and the film is primed with an ethylene acrylic acid copolymer to promote adhesion of the abrasive composite binder coating. Other backing materials include polyesters, polyolefins, polyamides, polyvinyl chloride, polyacrylates, polyacrylonitrile, polystyrene, polysulfones, polyimides, polycarbonates, cellulose acetates, polydimethyl siloxanes, polyfluocarbons, and blends of copolymers thereof, copolymers of ethylene and acrylic acid, copolymers of ethylene and vinyl acetate. Priming of the film includes surface alteration by a chemical primer, corona treatment, UV treatment, electron beam treatment, flame treatment and scuffing to increase the surface area. Solvents include those having a boiling point of 100 degrees C. or less such as acetone, methyl ethyl ketone, methyl t-butyl ether, ethyl acetate, acetonitrile, and one or more organic solvents having a boiling point of 125 degrees C. or less including methanol, ethanol, propanol, isopropanol, 2-ethoxyethanol and 2-propoxyethanol. Non-loading or load-resistant super size coatings can be used where “loading” is the term used in the abrasives industry to describe the filling of spaces between the abrasive particles with swarf (the material abraded from the workpiece) and the subsequent buildup of that material. Examples of load resistant materials include metal salts of fatty acids, urea-formaldehyde resins, waxes, mineral oils, cross linked siloxanes, cross linked silicones, fluorochemicals, and combinations thereof. Preferred load resistant super size coatings contain zinc stearate or calcium stearate in a cellulose binder. In one description, the make coat precursor can be partially cured before the abrasive grains are embedded into the make coat, after which a size coating precursor is applied. A friable fused aluminum oxide can be used as a filler.
U.S. Pat. No. 5,611,825 (Engen) describes resin adhesive binder systems which can be used for bonding abrasive particles to web backing material, particularly urea-aldehyde binders. There is no reference made to forming or abrasive coating abrasive islands. He describes the use of make, size and super size coatings, different backing materials, the use of methyl ethyl ketone and other solvents. Loose abrasive particles are either adhered to uncured make coat binders which have been coated on a backing or abrasive particles are dispersed in a 70 percent solids resin binder and this abrasive composite is bonded to the backing. Backing materials include very flat and smooth polyester film for common use in fine grade abrasives which allow all the particles to be in one plane. Primer coatings are used on the smooth backing films to increase adhesion of the make coating. Water solvents are desired but organic solvents are necessary for resins. Fillers include calcium metasilicate, aluminum sulfate, alumina trihydrate, cryolite, magnesia, kaolin, quartz, and glass. Grinding aid fillers include cryolite, potassium fluroborate, feldspar and sulfur. Backing films include polyesters, polyolefins, polyamides, polyvinyl chloride, polyacrylates, polyacrylonitrile, polystyrene, polysulfones, polyimides, polycarbonates, cellulose acetates, polydimethyl silotanes, polyfluorocarbons. Priming of the backing to improve make coating adhesion includes a chemical primer or surface alterations such a corona treatment, UV treatment, electron beam treatment, flame treatment and scuffing. Solvents include acetone, methyl ethyl ketone, methyl t-butyl ether, ethyl acetate, acetonitrile, tetrahydrofuran and others such as methanol, ethanol, propanol, isopropanol, 2-ethoxyethanol and 2-propoxyethanol. Abrasive filled slurry is coated by a variety of methods including knife coating, roll coating, spray coating, rotogravure coating, and like methods. Resins used include resole and novolac phenolic resins, aminoplast resins, melamine resins, epoxy resins, polyurethane resins, isocyanurate resins, urea-formaldehyde resins, isocyanurate resins and radiation-curable resins. Different examples of make, size and supersize coatings and their quantitative amounts of components were given.
U.S. Pat. No. 5,674,122 (Krech) described screen abrasive articles where the abrasive particles are applied to a make coat of phenolic resin by known techniques of drop coating or electrostatic coating. The make coating is then at least partially cured and a phenolic size coating is applied over the abrasive particles and both the make coat and size coat are fully cured. Make and size coats are applied by known techniques such as roll coating, spray coating, curtain coating and the like. Optionally, a super size coat can be applied over the size coat with anti-loading additive of a stearate such as zinc stearate in a concentration of about 25 percent by weight optionally along with other additives such as cryolite or other grinding aids. In addition, the abrasive coating can be applied as a slurry where the abrasive particles are dispersed in a resinous binder precursor which is applied to the backing by roll coating, spray coating, knife coating and the like. Various types of abrasive particles of aluminum oxide, ceramic aluminum oxide, heat-treated aluminum oxide, white-fused aluminum oxide, silicone carbide, alumina zirconia, diamond, ceria, cubic boron nitride, garnet and combinations of these in particle sizes ranging from 4 to 1300 micrometers can be used.
U.S. Pat. No. 5,733,175 (Leach) describes workpiece polishing machines with overlapping platens that provide uniform abrading velocities across the surface of the workpiece. Hydroplaning of workpieces during abrading action is discussed.
U.S. Pat. No. 5,888,548 (Wongsuragrai, et al.) discloses formation and drying of rice starches into 20 to 200 micron spherical agglomerates by mixing a slurry of rice flour with silicone dioxide and using a centrifugal spray head at elevated temperatures.
U.S. Pat. No. 5,910,471 (Christianson, et al.) discloses that the valleys between the raised adjacent abrasive composite truncated pyramids provide a means to allow fluid medium to flow freely between the abrasive composites which contributes to better cut rates and the increased flatness of the abraded workpiece surface.
U.S. Pat. No. 5,924,917 (Benedict) describes methods of making endless belts using an internal rotating driven system. He describes the problem of “edge shelling” which occurs on small width endless belts. This is the premature release of abrasive particles at the cut belt edge. He compensates for this by producing a belt edge that is very flexible and conformable. The analogy to this edge shelling occurs on circular abrasive disks also. To construct a belt, an abrasive web is first slit to the proper width by burst, or other, slitting techniques which tends to loosen the abrasive particles at the belt edge when the abrasive backing is separated at the appropriate width for a given belt. These edge particles may be weakly attached to the backing and they may also be changed in elevation so as to stick up higher than the remainder of the belt abrasive particles. Similarly, when a disk is punched out by die cutting techniques from a web section, the abrasive particles located on the outer peripheral cut edge are also weakened. This happens particularly for those discrete particles which were pushed laterally to the inside or outside of the die sizing hole by the matching die mandrel punch. Other types of cutting, slitting or punching abrasive articles from webs also create this shelling problem including water jet cutting, razor blade cutting, rotary knife slitting, and so on. Resole phenolic resins are alkaline catalyzed by catalysts such as sodium hydroxide, potassium hydroxide, organic amines or sodium carbonate and they are considered to be thermoset resins. Novolac phenolic resins are considered to be thermoplastic resins rather than thermoset resins which implies the novolac phenolics do not have the same high temperature service performance as the resole phenolics. Resole phenolic resins are the preferred resins because of their heat tolerance, relatively low moisture sensitivity, high hardness and low cost. During the coating process, make coat binder precursors are not solvent dried or polymerized cured to such a degree that it will not hold the abrasive particles. Generally, the make coat is not fully cured until the application of the size coat which saves a process step by fully curing both at the same time. Fillers include hollow or solid glass and phenolic spheroids and anti-static agents including graphite fibers, carbon black, metal oxides, such as vanadium oxide, conductive polymers, and humectants are used. Abrasive material encompasses abrasive particles, agglomerates and multi-grain abrasive granules. Belts are produced by this method using a batch process. The thermosetting binder resin dries, by the release of solvents, and in some instances, partially solidified or cured before the abrasive particles are applied. The resin viscosity may be adjusted by controlling the amount of solvent (the percent solids of the resin) and/or the chemistry of the starting resin. Heat may also be applied to lower the resin viscosity, and may additionally be applied during the processes to effect better wetting of the binder precursor. However, the amount of heat should be controlled such that there is not premature solidification of the binder precursor. There must be enough binder resin present to completely wet the surface of the particles to provide an anchoring mechanism for the abrasive particles. A film backing material used is PET, polyethylene terephthalate having a thickness of 0.005 inch (0.128 mm). Solvents used include trade designated aromatic 100 and Shell® CYCLO SO 53 solvent.
U.S. Pat. No. 6,017,265 (Cook, et al.) discloses abrasive slurry polishing pads that are used for polishing integrated circuits. He references polishing pads that are not highly flat and have variations in thickness where portions of the workpiece will not be in contact with the pad which gives rise to nonuniformities in the shape of the workpiece surface. A desirable thickness variation in these polishing pads is less the 0.001 inch (25 micrometers) in order to improve the uniformity of the polishing process.
U.S. Pat. No. 6,099,390 (Nishio, et al.) discloses abrasive slurry polishing pads having raised and recessed surfaces that are used for polishing semiconductor wafers. He references polishing pads that are used to polish semiconductors having level differences on the surface of the semiconductor wafer that are at most 1 to 2 micrometers.
U.S. Pat. No. 6,186,866 (Gagliardi) discloses the use of a abrasive article backing contoured by grinding-aid containing protrusions having a variety of peak-and-valley shapes. Abrasive particles are coated on both the contoured surfaces of the protrusions and also onto the valley areas that exist between the protrusion apexes. The protrusions present grinding aid to the working surface of the abrasive article throughout the normal useful life of the abrasive article. Useful life of an abrasive article begins after the abrasive particle coating that exists on the protrusion peaks is removed, which typically occurs within the first several seconds of use. Initial use, which occurs prior to the “useful life”, is defined as the first 10% of the life of the abrasive article. Protrusions contain a grinding aid, with the protrusions preferably formed from grinding aid alone, or the protrusions are a combination of grinding aid and a binder. The protrusion shapes have an apex shape that is coated with an adhesive resin and abrasive particles. The particles are drop coated or electrostatically coated onto the resin and thereby form a layer of abrasive particles conformably coated over both the peaks and valleys of the protrusion shapes. The primary objective of the protrusion shapes is to continually supply a source of grinding aid to the abrading process. There are apparent disadvantages of this product. Only a very few abrasive particles reside on the upper-most portions of the protrusion peaks and it is only these highest-positioned particles that contact a workpiece surface. The small quantity of individual particles contacting a workpiece, which are only a fraction of the total number of particles coated on the surface of the abrasive article, will be quickly worn down or become dislodged from the protrusion peaks. Particles would tend to break off from the protrusion wall surfaces, when subjected to abrading contact forces, due to the inherently weak resin particle bond support at individual particle locations on the curved protrusion walls. Abrasive particles are very weakly attached to the sloping sidewalls of the protrusions due to simple geometric considerations that make them vulnerable to detachment. It is difficult to bond a separate abrasive particle to a wall-side with a resin adhesive binder that does not naturally flow by gravity and symmetrically surrounds the portion of the particle that contacts the wall surface. Abrasive particles attached to a traditional flat-surfaced abrasive backing sheet article tend to have a symmetrical meniscus of resin surrounding the base of each particle but this configuration of meniscus would not generally form around a particle attached to a near vertical protrusion side-wall. Also, the protrusion side-wall is inherently weak as the protrusion body is constructed of grinding aid material. Much of the valuable superabrasive particles located in the valley areas are not utilized with this technique of particle surface conformal coating of both protrusion peaks and valleys. As the abrading action continues, with the wearing down of the erodible protrusions, more abrasive particles are available for abrading contact with a workpiece article. However, the advantage of having protrusion valleys, that are used to channel coolant fluids and swarf, disappears as the valleys cease to exist. The procedure cited for testing the protrusion contoured abrasive article cited the use of a 7 inch (17.8 cm) diameter disk operated at approximately 5,500 rpm indicating an intended high surface speed abrading operation. FIG. 23 (Prior Art) is a cross section view of the Gagliardi abrasive coated raised island protrusion structures. The protrusions 254 that are attached to a backing sheet 256 are coated with abrasive particles 252. There is no description of precisely controlling the height of the abrasive or of the protrusions as measured from the backside of the backing 256. FIG. 24 (Prior Art) is a cross section view of rectangular-walled Gagliardi abrasive coated raised island protrusion structures. The protrusions 258 that are attached to a backing sheet 264 are coated with abrasive particles 260. There is no description of precisely controlling the height of the abrasive or of the protrusions as measured from the backside of the backing 256 as shown by the dimension 262.
U.S. Pat. No. 6,217,413 (Christianson) discloses the use of phenolic or other resins where abrasive agglomerates are drop coated preferably into a monolayer. Leveling and truing out the abrading surface is performed on the abrasive article which results in a tighter tolerance during abrading.
U.S. Pat. No. 6,231,629 (Christianson, et al.) discloses a slurry of abrasive particles mixed in a binder and applied to a backing sheet to form truncated pyramids and rounded dome shapes of the resin based abrasive particle mixture. Fluids including water, an organic lubricant, a detergent, a coolant or combinations thereof are used in abrading which results in a finer finish on glass. Fluid flow in valleys between the pyramid tops tends to produce a better cut rate, surface finish and increased flatness during glass polishing. Presumably, these performance advantages would last until the raised composite pyramids or domes are worn away. Abrasive diamond particles may either have a blocky shape or a needle like shape and may contain a surface coating of nickel, aluminum, copper, silica or an organic coating.
U.S. Pat. No. 6,299,508 (Gagliardi, et al.) discloses abrasive particle coated protrusions attached to a backing sheet where the protrusions have stem web or mushroom shapes with large aspect ratios of the mushroom shape stem top surface to the stem height. A large number of abrasive particles are attached to the vertical walls of the stems compared to the number of particles attached to the stem top surface. Abrasive discs using this technology range in diameter from 50 mm (1.97 inches) to 1,000 mm (39.73 inches) and operate up to 20,000 revolutions per minute. As in Gagliardi, U.S. Pat. No. 6,186,866, the abrasive article described here does not provide that the attachment positions of the individual abrasive particles are in a flat plane which is required to create an abrasive article that can be used effectively for high surface speed lapping.
U.S. Pat. No. 6,319,108 (Adefris, et al.), herein incorporated by reference, discloses the electroplating of composite porous ceramic abrasive composites on metal circular disks having localized island area patterns of abrasive composites that are directly attached to the flat surface of the disk. Glass-ceramic composites are the result of controlled heat-treatment. The pores in the porous ceramic matrix may be open to the external surface of the composite agglomerate or sealed. Pores in the ceramic mix are believed to aid in the controlled breakdown of the ceramic abrasive composites leading to a release of used (i.e., dull) abrasive particles from the composites. A porous ceramic matrix may be formed by techniques well known in the art, for example, by controlled firing of a ceramic matrix precursor or by the inclusion of pore forming agents, for example, glass bubbles, in the ceramic matrix precursor. Preferred ceramic matrixes comprise glasses comprising metal oxides, for example, aluminum oxide, boron oxide, silicone oxide, magnesium oxide, manganese oxide, zinc oxide, and mixtures thereof. A preferred ceramic matrix is alumina-borosilicate glass. The ceramic matrix precursor abrasive composite agglomerates are fired by heating the composites to a temperature ranging from about 600 to 950 degrees C. At lower firing temperatures (e.g., less than about 750 degree C.) an oxidizing atmosphere may be preferred. At higher firing temperature (e.g., greater than about 750 degree C.) an inert atmosphere (e.g., nitrogen) may be preferred. Firing converts the ceramic matrix precursor into a porous ceramic matrix. An organic size coat comprising resole phenolic resin (the resole phenolic was 78% solids in water and contained 0.75-1.8% free formaldehyde and 6-8% free phenol), tap water, silane coupling agent and a wetting agent may be coated over the ceramic abrasive composites and the metal coatings on an abrasive article. Individual diamond particles contained in the composites have metal surface coatings including nickel, aluminum, copper, inorganic coatings including silica or organic coatings. Composite abrasive agglomerates sink through an electroplating solution and land on a conductive backing where they are surrounded by plated metal that bonds the agglomerates to the backing surface. A polymer size coat can be applied over the agglomerates to strengthen the bond attachment of the agglomerates to the backing. Composites may have a mixture of different sizes and shapes but there is a stated preference that the abrasive composites have the same shape and size for a given abrasive article. Diamond particles were mixed with metal oxides to form an aqueous slurry solution that was coated into cavities, solidified, removed from the cavities and at 720 degrees C.
U.S. Pat. No. 6,371,842 (Romero) describes island-type abrasive grinding disk articles that have an article center aperture hole and circular bands of raised islands having flat top surfaces that are adhesive coated and abrasive particles which are deposited onto the adhesive. The raised island abrasive hand tool disks disclosed by Romero are intended to correct a specific problem that occurs in typical non-island disk manufacturing where thick preformed disks are coated with an adhesive binder that has a tendency to form a high lip of binder coating on the disk backing outer peripheral edge, after which, abrasive particles are deposited on the binder raised peripheral lip. This raised elevation outer diameter raised lip that is coated with abrasive particles causes undesirable workpiece surface scratches during abrading use. The use of abrasive coated raised island structures that are attached to a backing sheet reduces the formation of the raised abrasive peripheral edge lips on manual tool grinding disk articles. FIG. 12 (Prior Art) is a top view of a Romero described abrasive disk that has an outer periphery polymer adhesive make-coat raised band. The disk 130 has a disk-center aperture hole 134 and a raised polymer peripheral band 132 where both the flat surface of the disk 130 and the outer band 132 are surface coated with abrasive particles 140. FIG. 13 (Prior Art) is a cross section view of a Romero described abrasive disk having a raised polymer band on the outer periphery of the disk. The disk backing 144 has a coating of polymer adhesive 142 that is generally flat across the inner surface of the disk but the polymer adhesive 142 has a outer periphery raised-bead edge 138 where all the adhesive 142 in both the disk 144 flat inner area surface and the top surface of the bead edge 138 has a coating of abrasive particles 136. FIG. 14 (Prior Art) is a top view of a Romero described disk having abrasive coated raised islands. The disk 152 has a center aperture hole 150 and a number of abrasive particle coated raised island structures 148 that are positioned radially on the disk 152 where the inner radius position of all the raised islands 148 have a common island 148 end-position inner radial location diameter 146. The radial islands 148 each have a radial length that is somewhat less than the radius of the disk 152. No teaching is included of the advantage of having the radial islands 148 having a minimum position diameter 146 to reduce the large change of surface cutting speeds of the radial disk from the inner radius portions of the radial islands 148 to the outer radius portions of the radial islands 148. Romero focuses on an abrasive article that has raised islands where there are gap spaces between the islands and the outer periphery of the backing sheet. His use of abrasive coated raised islands that are positioned a gap-distance away from the peripheral edge of the backing sheet is a solution to the addressed problem of the raised peripheral edge bead of abrasive particle coated resin. He does not disclose abrasive articles where the raised islands are positioned directly at the outer periphery of the abrasive article backing sheet without a gap between the raised islands and the backing sheet. His abrasive islands also are adhesive coated on the top island surface only and abrasive particles are drop coated on the island adhesive coated surfaces to form abrasive particle coated islands, and where the recessed valley areas between the raised islands do not have abrasive particles. No other raised island abrasive particle coating techniques, such as applying an abrasive resin slurry directly onto the island top surfaces, are described.
The Romero abrasive disk articles described are not suggested for nor is awareness indicated for their use in flat lapping or in flat grinding where the disks would be mounted on a flat surfaced rotary platen. Instead the articles are taught to be mounted on hand tool mandrels by the use of mechanical fasteners that penetrate an aperture hole located at the center of the circular disk. No mention or teachings are made of the art of precision flat grinding, or lapping, of flat workpiece surfaces or of using these island disks in that abrasive application area. Also, there is no mention of the precision control of the variation in the thickness of the abrasive disk articles or the use of the precision flatness grinding or lapping machines that are required to produce precise flat workpiece surfaces. There is no mention of the desirability of the existence of a mono (single) layer of coated abrasive particles; or of controlling the variation of the thickness of the abrasive article to a proportion of the diameter of the coated abrasive particles. Further, no mention is made of the problems of hydroplaning of disks or workpieces.
Romero does not teach the advantages or requirements of having the features of uniform flat surfaces or even “substantially planar surfaces” for: the recessed valley areas located between the islands; the top surfaces of the islands; or the back side surface of the backing in the non-claims portion of the patent specification. There is no reference given for the use of the island type abrasive articles to be used for creating precision flat workpiece surfaces or precise smooth workpiece surfaces as in a flat-lapping operation. Flat lapping requires extremely flat abrasive disk machine tool platens and the abrasive disk article also must be precisely flat and of uniform thickness to enable all of the coated abrasive particles to be utilized. Further, there is no mention of the advantages of arranging the raised islands in an annular array having a narrow outer radius annular band width of abrasive to avoid having the slow moving abrasive surfaces that are located at the inner diameter area of a disk, to be in contact with a workpiece surface. Uneven wear occurs across the surface of a workpiece when the workpiece is in contact with an abrasive article abrading surface that has both fast and slow surface speeds. Reduced workpiece material removal occurs at the inner diameter area of an abrasive disk, which is slow moving, while the majority of the material removal occurs at the outer diameter area of the disk, which has the highest surface speed area.
Romero's abrasive disks have significant amounts of fibers and other fillers imbedded in the disk backing which tends to produce a disk of limited thickness uniformity. The preferred embodiment of Romeo is a thick fiber filled disk backing. These thick and very stiff abrasive disks generally require “flexing” after manufacturing where portions, or all of, the disk is bent through a out-of-plane angle sufficient that the thick disk is fractured, resulting in many small cracks through the disk thickness. The crack-fractured disk is weaker structurally than a non-cracked disk and has less disk article stiffness, thereby providing a more flexible disk that can more readily conform to a workpiece surface. The backings used for the Romero disks are not as thick as the traditional disk backings and he states that it is not necessary to do the Flex-bending” of his raised island disks to provide a disk having sufficient flexibility. He states that thin backings having a backing thickness of from 100 micrometers (0.004 inches) to 2500 micrometers (0.100 inches) are too thin and will easily rip and tear when used in his abrading application. The Romero disks are intended for use with manual grinding tools where the amount of workpiece material removal is of primary concern, rather than controlling the flatness of the workpiece. This type of grinding disk generally would have large sized abrasive particles that are not suitable for polishing or lapping operations. The described abrasive disk is frictionally mounted to a flexible backup pad that is attached to a mandrel with a disk-center-screw-cap that penetrates the disk-center aperture hole and squeezes the disk against the flexible and conformable metal or polymer backup pad. The screw-cap mounting forces result in significant and uneven distortions of both the abrasive disk sheet and the backup pad prior to the moving abrasive contacting a workpiece. Mounting a thin and fragile 0.004 inch (100 micrometer), or less, thick polymer abrasive island backing sheet to a manual abrading tool with a disk-center screw flange to a flexible padded mandrel can easily crease or tear the thin polymer backing in the area of the flange screw where large localized distortions of the backing can take place. Tearing of these thin disk sheets can occur at the outer radius location on a abrasive disk article particularly as the outer radial portions of the thin backing sheet are not attached to the stronger flexible abrasive tool disk pad that is used as a back-up support for the compressive forces (only) that are applied to the abrasive disk article. Abrasive disks used on these types of manual or machine abrasive tools encounter large tangential forces when contacting a workpiece during abrasion action and there is little strength in the independent loose fitting thin disk backings to resist these tangential forces. Grinding disks having thick fiber-reinforced backing sheets can easily resist these large tangential abrading contact forces as these thick disks are very strong in a tangential direction. Also, tearing of thin backing sheet disks would tend to occur at the disk center. Here, the thin disk is attached at the disk center aperture hole area only where a flat surfaced internally threaded attachment nut, or threaded attachment cap, holds the disk in pressure contact with the abrasive tool flexible back-up pad. Frictional contact between the disk sheet and the attachment nut occurs at only the small outer radial surface area of the diameter of the nut. The outside-flat surfaced nut is tightened by manually rotating the abrasive disk, and the nut, against the manual tool hold-down screw post, which is temporarily held stationary during this disk mounting procedure. Only a very narrow annular band of the flexible and fragile thin abrasive disk at the disk center is in contact with the nut inside annular surface, which, in itself, is not necessarily flat. When the abrasive disk attachment nut inside annular surface is not flat, or the abrasive disk nut-contact annular surface is pressured into a location not parallel with the plane of the abrasive tool flexible mounting pad, the flexible abrasive disk is distorted into a out-of-plane configuration, particularly at the location of the disk center. Out-of-plane distortions that are localized can create stress-risers within the thickness of the disk sheet. These stress risers can multiply any backing material stresses due to abrading forces that are transmitted to this critical center area of the disk, where the disk is attached to the abrasive tool. The narrow annular band of the abrasive disk that is in contact with nut is then subjected to a significant portion of the mounting nut tightening torque force when the disk is attached to the tool, depending how the tightening force is applied to the abrasive disk. Tightening of the nut progresses until the resulting mounting nut disk center compressive force is significantly high to compress and distort the abrasive tool thick flexible backing pad sufficiently to provide a secure attachment of the disk and pad to the manual abrading tool. A thin abrasive disk article can be easily torn at the abrasive disk center just by this disk attachment mounting procedure. Also, a significant portion of the torque dynamic impact forces that act in a tangential location at the outer periphery of the disk, as a result of the disk contacting a workpiece at the disk periphery during disk abrading procedures, can be transmitted to the disk center where the disk is attached to the small center attachment nut. A disk center mounted thin flexible polymer disk backing has little strength at its center to resist these outer radius tangential forces and will tend to tear at the disk center mounting location as a result of these forces. There is little additional strength that is provided to the thin abrasive disk article backing sheet by the polymer binder that is used to bind the abrasive particles to the backing as this binder layer also is so thin. As a reference, the backing thicknesses typically used for abrasive lapping articles are from 50 to 100 micrometers (0.002 to 0.004 inches) thick and by comparison to grinding disks, these lapping sheet articles are very delicate and fragile. The lapping sheet abrasive articles typically use thin backings sheets that are coated with single-layer abrasive binder coatings to attach 0.002 inch (51 micrometer) diameter abrasive agglomerate beads to the backings. Lapping sheet abrasive articles that use these thin polymer backings and thin abrasive binder coatings of abrasive materials are used successively for abrasive flat lapping procedures without tearing problems. These lapping sheet abrasive articles are mounted differently to a lapping machine head than are abrasive disks mounted to a manual abrasive tool. First the abrasive disk is not attached to a platen only with a disk-center torque tightened threaded device. Instead the flexible abrasive disk sheet is attached to a flat platen with the use of vacuum which applies a hold-down force pressure of nearly one atmosphere (14.7 lbs/sq. inch) to all of the flat surface of the abrasive article. A typical abrasive disk has a large surface area which results in a very large total disk hold down attachment force. There is no distortion of the abrasive disk out-of-plane from the original-condition disk surface as the platen is flat and the flexible abrasive disk easily conforms to the flat platen with no localized stress-risers in the disk backing material. Forces that are applied at the abrasive disk outer periphery tend to remain in the outer disk areas where they are applied as they are not transferred to the central area of the disk. These disk outer periphery forces are also not multiplied as they are transmitted to the inner radius of the disk due to the geometry factor where a force applied at the large radius at the periphery increases as a function of being transferred to, and concentrated at, a disk center small radius. Further, there is no multiplication of the disk backing abrading force stresses due to the disk sheet buckling that can occur when a disk sheet experiences a localized out-of-plane distortion. An abrasive disk that is held to the surface of a platen has a significant coefficient of friction between the disk surface and the platen surface and the disk mounting surface friction resists movement of the abrasive disk sheet relative to the platen surface. The coefficient of friction between the abrasive disk and the platen can be enhanced by surface coatings, etching or otherwise surface conditioning of either the surfaces of the abrasive disk backing or of the platen surface, or both. The Romero backing sheet has integral raised islands that is constructed by a variety of techniques including: 1.) molding a flat disk with integral raised islands; or 2.) adhesively bonding island shapes cut out from sheet material to a backing disk; or 3.) embossing island shapes into the surface of a flat backing disk sheet. None of these three raised island disk manufacturing techniques would be expected to produce islands having precisely flat surfaces where the island height variations, as measured from the backside of the backing, is within the 0.0001 to 0.0003 inch (0.003 to 0.008 mm) tolerance that is typically required for 8,000 or more surface feet per minute SFPM high speed platen flat lapping. Romero does not teach the use of a circular disk backing that does not have a center hole aperture in the non-claims portion of the patent specification. He describes raised island abrasive substrate sheets or strips having rectangle, square, hexagon, octagon and oval shapes. However, these non-circular strip shapes, which are presumed to be used with sheet-center aperture holes (the same as for aperture-hole circular disks) allow multiple layers of these non-circular abrasive strip sheets to be mounted on a mandrel. Here, the cut-out abrasive strips are positioned with incremental rotational angles about the aperture hole position relative to each other in a manner that all the stacked strips mutually form a circular disk shaped abrasive article when they are mutually attached to a mandrel with an aperture screw-cap. However, each of the composite abrasive strips lays at a different elevation relative to each other due to the stacking of individual strips, which means that a continuous abrasive surface can not be presented to a workpiece surface. Instead the abrading action takes place primarily at the trailing edge of the single outermost strip that is in contact with a workpiece. This type of abrasive article typically can have large sized abrasive particles relative to the thickness of the backing sheets, even though the backing sheets are very thick. This type of abrasive article is only suited for rough grinding, not for flat lapping. Romero incorporates by reference U.S. Pat. No. 5,142,829 (Germain) which describes a variety of these same types of non-circular abrasive sheet shapes, all having center aperture holes, where the holes allow them to be progressively stacked on a mandrel for use as a flapper abrasive portable manual tool. Romero does not disclose flat sheets, long strips or belts of abrasive coated raised island articles that do not have a disk-center aperture hole or disclose where these disks would be used for non-manual tool abrading purposes. Disk articles that have disk-center aperture holes are used principally on portable tool mandrels. The method described by Romero for coating the abrasive disk with abrasive particles is to first coat the island top surfaces with a make coat of binder, deposit loose abrasive particles on the make coat and then add a size coat of binder after which the binders are cured. Coating the island top surfaces with an abrasive slurry is not taught. It is important that raised island structures do not exist in the center area of the abrasive disk as the screw flange nut, or threaded nut, would contact parts of the raised island structures, thereby making it difficult to attach an abrasive disk to a grinder tool head under this condition. Romero does specify a disk center area that is free of the raised island structures.
Romero does not teach the hydroplaning of workpieces surfaces when lapping at very high surface speeds. Hydroplaning would not be an issue when using a abrasive disk on a mandrel tool device as the abrasive article would have a line-shaped area of contact with a workpiece surface due to the abrasive article out-of-plane distortion by the tool operator. A water boundary layer does not build up in thickness and create hydroplaning for line-contact abrading surfaces because there is not enough distance for the water film to increase in thickness across the short distance of the line width. Also, there is a very highly localized area of contact pressure at the abrading contact line area due to the large applied pressure that is distributed over a very small area. Most of the manual force applied by a mandrel to an abrasive disk is concentrated at the small line-area where the abrasive disk is distorted most where it contacts a workpiece surface. This high contact line-area pressure tends to prevent the boundary layer thickness buildup of coolant water. In the instance of flat lapping, the abrasive contacts the workpiece with a very low contact force across a full surface area that is typically as wide as the width of the workpiece. Due to the low contact force and large contact area, the water boundary layer can build up in substantial thickness across the relatively long distance that extends across the full length of the mutual abrading contact area. In this way, hydroplaning, where a portion of the workpiece is lifted from the abrasive surface by the depth or thickness of the water boundary layer, does not tend to occur for mandrel-and-flexible-pad type of manual tool abrading. Hydroplaning is difficult to avoid for machine tool flat lapping at high surface speeds.
Island types of abrasive articles used for precision flat grinding or lapping are primarily suited for use with rotating flat platen surfaces. The localized individual island sites are structurally stiff due to their increased thickness as compared to the thickness of the adjacent thin backing sheet. The flexural stiffness of the island areas is a function of the total island material thickness cubed, which means a relatively small change in the backing sheet material thickness at the location of a raised elevation island can change the localized stiffness of the island area by a very large amount. These abrasive coated stiff islands will not easily conform to a curved surface. Stiff raised large diameter islands that have a thin flat top surface coating of abrasive material will only be contacted by a workpiece at the central portion of the island abrasive or in a line extending across the surface of an island when contacting a convex workpiece. Only the abrasive outer island peripheral edges of a stiff island would be contacted when abrading a concave workpiece. In either case, abrading action results in uneven wear of both the island coated abrasive and of the workpiece surface. In a like manner, raised island abrasive disk articles having stiff islands that have their flat disk-plane surface distorted by manual pressure when contacting a flat workpiece will only be effective in uniform material removal if the island dimensions are very small, in particularly the tangential direction. Here, small islands can lay flat to a workpiece but only if the adjacent disk backing material that is located next to the islands is flexible enough to allow the island to bend enough to compensate for the disk out-of-plane distortion created by the abrasive tool operator. Even if the backing is flexible, the backing pad would tend to prevent this conforming action. Stiff and thick backings are generally used with manual abrasive disk articles as thin backings are too fragile for this type of abrading usage. Manual pressure will distort the disk plane in both a radial and tangential direction. This abrasive sheet distortion would prevent the production of a precision flat workpiece surface with this manual apparatus and abrasive article. Flexible sheets of a non-island uniform coated abrasive article having a thin backing will conform to a flat rigid platen which provides a natural flat abrading surface for the whole surface of the abrasive sheet. The thin and flexible and structurally weak lapping sheets assume the flat surface of the platen even if the lapping sheet is not perfectly flat prior to contact with the platen. Vacuum is typically employed to bring the thin lapping sheet into intimate contact with the platen and to hold the abrasive lapping sheet in flat contact with the platen even when the lapping sheet is subjected to significant contact pressures and forces during the abrading action. Likewise, a thin backing sheet or disk having integral raised islands will likewise conform to the flat platen surface where each of the individual islands will be presented with a flat island top surface that is mutually flat to the workpiece surface. Flexible abrasive sheets or disks having raised islands mounted on flat platens can be used effectively for the flat grinding and smooth lapping of a flat workpiece surfaces. The Romero described abrasive disks as used with conformable screw-cap mandrel pads are not practical for use for precision flat grinding. Conformable pad mandrels are generally used on portable grinding tools that are held with large (6 kilogram or 13 lbs) manual contact forces against a workpiece. This large force typically deforms a portion of the flexible abrasive disk supporting pad to allow an controlled area of the thick and stiff abrasive disk to be in flat contact with a workpiece surface. The whole large contact force tends to be concentrated at the typical small line-type contact area that exists between the abrasive and the workpiece surfaces. The manual abrasive grinding operator typically moves the disk with a random oscillation-type orientation motion relative to the surface of the workpiece. In the comparative case of a flat lapping machine, a low contact force of 1 to 2 lbs (0.5 to 1 kg) is spread evenly over large surface areas of a workpiece having a 3 inch (76 mm) diameter that is supported by a workpiece holder spindle. The workpiece spindle of a flat lapping machine is typically orientated perpendicular to the surface of an abrasive disk that is flat mounted to a rigid platen. A manual abrasive disk tool is typically oriented at a significant angle to the workpiece surface. Very low stresses are induced within the thin and weak abrasive backing sheet used in flat lapping because the relatively large mutual flat workpiece and abrasive contact surface areas do not create localized areas of abrading contact forces. Thin backings as used with the manual tool grinding pad disks is stated by Romero to be a problem as this fragile type of disk easily rips and tears and can crease and pucker the disk article.
FIG. 15 (Prior Art) shows an expanded side view of the FIG. 10 (Romero, and others) abrasive disk that is mounted on a mandrel tool used to grind a workpiece with the disk distorted. The abrasive disk 160 that has attached islands 162, which have a coating of abrasive 164. The abrasive 164 that is located at the edge of the island 162 contacts the workpiece 168 at a contact point 166. When the abrasive 164 contacts the workpiece 168 at a single point 166 during abrading action, the workpiece can be scratched at this single point-contact, rather than the workpiece 168 being polished at this location by the abrasive 164. This scratching occurs because the abrasive disk 160 having abrasive 164 coated islands 162 is typically presented at an angle to the workpiece rather than the abrasive 164 on all the islands 162 being presented in flat contact with the workpiece 168 surface. Mounting of a disk 160 by use of a disk-center threaded screw device with a flexible pad to a hand-tool mandrel tends to prevent all of the flat contact surfaces of the abrasive 164 coated raised islands 162 from lying in a flat plane relative to the workpiece 168 flat plane surface due to distortion of the disk 160 by the threaded screw device, not shown. Any out-of-plane contact of the abrasive 164 with the workpiece 168 will tend to create workpiece 168 scratches. This makes it impractical to use these abrasive disks on manual tool disk mandrel systems to provide flat lapping of workpieces. However, these abrasive disks and mandrels are suitable for rough grinding of a workpiece. FIG. 16 (Prior Art) shows an expanded side view of a (Romero, and others, as shown in FIG. 15 single abrasive coated island in angled contact with a flat workpiece. The island 170 having an abrasive coating 176 is positioned at an angle 177 with a workpiece 172 where the leading-edge contact portion of the island 170 and the abrasive 176 both independently contact the workpiece 172. The island structural material contacts the workpiece at the contact point 174. It is typically not desirable for the island non-abrasive structural material to contact a workpiece surface during abrading, especially for precision flat lapping, as the abrading characteristics, or workpiece contamination action, of this island 170 structural material may be unknown. The leading edge of the abrasive 176 also makes a sharp-edge contact area 178 with the workpiece 172. The expanded view of this figure shows a significant sized abrasive 176 contact area 178 even though the area 178 is actually quite small, as the island surface abrasive 176 coating thickness 173 is typically less than 0.002 inches (50 micrometers) for an abrasive lapping article. FIG. 17 (Prior Art) is a cross section view of Romero abrasive coated islands attached to a backing sheet. Raised island structures 186 are coated with a layer of adhesive 184 with abrasive particles 180 and 182 that are deposited onto, or applied to, the adhesive 184 coating. The islands 186 are attached to a backing sheet 187 and a gap 192 exists between the outer edge of the island 186 and the outer periphery 193 of the backing 187. There is no disclosure of control of the relative height (or island height variations) of the island structures 186 as shown by the height variation dimension 188. There is also no control of the thickness or size 190 of the abrasive particles 182 or control of the height of the island structure 186 height 194 as measured from the top of the adhesive 184 coated island 186 and the backside of the backing sheet 187. Also, there is no control of the height of the abrasive particle 182 coated island 186 island structure thickness 195 as measured between the top of the abrasive particles 182 and the backside of the backing sheet 187. FIG. 18 (Prior Art) is a top view of Romero abrasive island disk having an aperture hole and an island gap at the disk periphery. The disk 200 has a disk-center aperture hole 198 that allows the disk 200 to be screw fastener mounted to a manual abrasive grinder tool, not shown. The abrasive coated raised islands 202 have a recessed area gap having a gap-width dimension 204 where this recessed gap extends around the outer periphery of the disk 200 between the edges of the islands 202 and the disk 200 edge. Romero also describes the abrasive particle re-coating of his worn-out abrasive raised island disks. Island structures that are worn down in abrading use are re-coated with an adhesive layer on top of the worn island structures and abrasive particles are deposited on the raised island adhesive layers. After sufficient adhesive is applied to structurally support the individual abrasive particles on the island tops, the adhesive is fully cured to develop the adhesive bond strength. The disk is then appraised by Romero to be suitable for his intended abrading use. It is obvious that this abrading use is not precision grinding or precision flat lapping. All of the mutual-plane flatness, if it originally existed, of the individual abrasive coated islands would have been lost in the first abrading usage of the disk and this lack of flatness would have been retained in the re-coating procedure. It is very difficult to obtain an even or flat in-plane wear of a circular abrasive disk due to the fact that the outer radius of the disk has a higher rate of surface speed than the inner radius of the disk and the disk abrasive will wear down at a faster rate at high surface speeds than at low surface speeds. Other localized areas of the original disk will wear down at faster rates due to causes including, but not limited to, the disk-surface variations in the contact force that is applied between the abrasive disk and the workpiece surface. Abrasive wear rates increase for higher contact forces. (Prior Art) is a cross section view of a precisely flat original-condition Romero abrasive island FIG. 19 article. Raised island structures 214 are attached to a disk backing sheet 218 where the islands 214 have a top layer coats of adhesive 212 which binds abrasive particles 210 to the islands 214. All of the abrasive particles 210 that are positioned at the top of each of the islands 214 are shown to lie in a mutual flat plane 216 that is parallel to the backside of the backing 218. FIG. 20 (Prior Art) is a cross section view of the precisely flat original-condition Romero abrasive island article shown in FIG. 19 that has been subjected to abrading wear where all of the adhesive and abrasive particles that were originally attached to the island top surfaces are worn down. The worn-down island structures 220, 222, 223, and 224 originally had a mutual-plane 226 height location that was parallel to the backside of the backing sheet 228. After partial wear-down of the island structures, the islands 222, 223 and 224 all have top surfaces that lie in a mutual angled plane 225 that is not parallel to the backside of the backing sheet 228. Likewise the top surface of the island 220 is ground to a shape that lies in a different plane 221 and that plane 221 is neither parallel to the backside of the backing 228 or parallel to the plane 225. FIG. 21 (Prior Art) is a cross section view of the worn-down islands on the backing shown in FIG. 20 that have been recoated with adhesive and abrasive particles. The islands 234 are coated with an adhesive 232 that bonds abrasive particles 230 to the top surfaces of the worn-down islands 234. The abrasive 230 coated island 234 surfaces lie in two different planes 231 and 235 where plane 235 is not parallel to either the original island top surface flatness plane 236 or the island 234 plane 231. In addition, all of the islands 234 have different top surface height locations where the island heights are measured from the backside of the backing sheet 240. In order for the abrasive article to be useful for precision flat grinding or flat lapping, each abrasive coated island on a backing sheet must have the same height elevation relative to the backside if the backings, and also, the top surface of each island must also be flat in a island-mutual plane that is parallel to the backside of the backing 240.
U.S. Pat. No. 6,521,004 (Culler, et al.) and U.S. Pat. No. 6,620,214 (McArdle, et al.) disclose the manufacturing of abrasive agglomerates by use of a method to force a mixture of abrasive particle through a conical perforated screen to form filaments which fall by gravity into an energy zone for curing. U.S. Pat. No. 4,773,599 (Lynch, et al.) discloses an apparatus for extruding material through a conical perforated screen. U.S. Pat. No. 4,393,021 (Eisenberg, et al.) discloses an apparatus for extruding a mix of grit materials with rollers through a sieve web to form extruded worm-like agglomerate lengths that are heated to harden them.
U.S. Pat. No. 6,540,597 (Ohmori) describes a raised island polishing pad conditioner that reconditions pads that are used to polish silicone wafers. The raised island structures are coated with abrasive particles.
U.S. Pat. No. 6,551,366 (D'Souza et al.) describes the manufacture of spherical abrasive agglomerate beads by spray drying an abrasive particle, a binder and water mixture in a rotary spray dryer.
U.S. Pat. No. 6,602,439 (Hampden-Smith et al.) and U.S. patent application No. 2002/0003225 (Hampden-Smith et al.) describes the manufacture and use of composite abrasive beads made from slurries of abrasive particles and water soluble salts and other metal oxide water based materials. He introduces the abrasive slurry liquid onto the surface of an ultrasonic head aerosol generator operating at 1.6 MHz (1.6 million cycles per second) to produce 0.1 to 2 micron nominal sized droplets. Also, the ultrasonic heads simultaneously produce a range of other droplets having sizes of mostly less than 5 microns. Here, the abrasive slurry liquid covering the ultrasonic head forms standing slurry waves where the tips of the liquid waves shed droplets that are introduced into a hot air environment where they are solidified. These droplets form abrasive spheres, but again, the spheres have a large variation in size. Droplets are classified or separated by size when they are still in a liquid state by introducing them, after ultrasonic generation, into a moving air stream that is routed at sharp angles between barrier plates. The oversized droplets can't follow the sharp air-turns and impact a barrier wall. The wall impacted droplets change into a liquid that runs down the wall and is collected in a drainpipe. Those spherical slurry droplets that have the desired size are then subjected to heating to first solidify them. Then individual beads are heat treated in a furnace into a single crystal or into a number of crystals or into a amorphous bead. The small 2 micron abrasive spheres produced are used in chemical mechanical planarization (CMP) polishing of workpieces. He can incorporate the chemically active compound ceria into the beads. Ceria is commonly used for polishing technical glasses as it can accelerate the removal of silica by chemically reacting and bonding with the silica surface. The abrasive beads can individually include both CeO2 and SiO2. No mention is made of using lower ultrasonic frequencies in the range of 20,000 Hz that would typically produce droplets of the much larger 45 micron size which is the abrasive bead size that is desired for resin-bond coating onto backing sheets to form fixed-abrasive sheet or disk articles. Droplets produced by ultrasonic heads vary in size, in part, as a function of the oscillation frequency of the ultrasonic head where higher frequencies produce smaller droplets. However, an ultrasonic atomization head always simultaneously produces a wide range of droplet sizes.
U.S. Pat. No. 6,613,113 (Minick et al.) describes island-type flexible abrasive bodies covered with abrasive particles that are attached to a flexible backing sheet.
U.S. Pat. No. 6,645,624 (Adefris, et al.), herein incorporated by reference, discloses the manufacturing of spherical abrasive agglomerates by use of a high-speed rotational spray dryer to dry a sol of abrasive particles, oxides and water. An abrasive slurry of abrasive particles mixed in a Ludox® colloidal silica water solution is introduced into the center of a rotating wheel operating at 37,500 revolutions per minute (RPM) where centrifugal action drives the slurry to the outside diameter of the wheel where it exits the wheel into a dehydrating environment of hot air. Typically, when using rotary atomizers, individual slurry streams exit spaced ports located at the wheel periphery and form into thin curved string-like or ligament streams of fluid at each port where the streams have both a large tangential and radial fluid velocity. These individual curved slurry streams are separated into a stream pattern of adjacent individual droplets as the high speed stream moves through the stationary air. The droplets are then drawn into spheres by surface tension forces acting on the free-falling drops. Sphere sizes of the drops are controlled, in part, by adjusting the wheel rotation RPM. The slurry drops are formed into solidified abrasive beads by the dehydrating action of the hot air. Again, there is a wide distribution of abrasive sphere sizes produced by this method. Abrasive beads can also be formed by simply spraying a slurry mixture, from a paint sprayer type of spray device or other pressurized nozzles, into a dehydrating fluid (either hot air or a liquid bath) but the range of droplets sizes produced by these devices would vary considerably.
U.S. Pat. No. 6,752,700 (Duescher) and U.S. Pat. No. 6,769,969 (Duescher) describe island-type abrasive lapping or grinding flexible abrasive articles that have an precision height raised island structure that is coated with abrasive particles or abrasive agglomerate beads. The height of both the island structure and the top surface of the abrasive beads as measured to the backside of the backing sheet are controlled with a height variation of less than a percentage of the diameter size of the abrasive beads. The precision control of the height or elevation of the abrasive beads allows these abrasive articles to be used to abrade workpiece surfaces where all of the abrasive material coated on the islands is utilized when the abrasive article is mounted on a precision flat platen or other type mounting surface. The raised island structures allow excessive coolant water to flow in the recessed channels that exist between the raised islands, which minimizes the occurrence of hydroplaning of the workpiece during a high surface speed lapping operation. Reduction of hydroplaning effects improves producing a precisely flat workpiece surface. The recessed channels that exist between the island structures also allow grinding debris to be washed out from the workpiece abrading contact area by coolant water, which prevents workpiece surface scratching that can occur when this loose debris becomes lodged between the workpiece and the abrasive article surface. FIG. 26 is a cross section view of a non-abrasive coated raised island structure 300 that is attached to a flexible backing sheet 302. FIG. 27 is a cross section view of an adhesive 306 coated raised island structure 304 that is attached to a flexible backing sheet 308. FIG. 28 is a cross section view of an adhesive 312 coated raised island structure 314 that is attached to a flexible backing sheet 316 where abrasive agglomerate beads 310 containing abrasive particles 311 are supported by the adhesive 312. FIG. 29 is a cross section view of an abrasive article 324 having adhesive 320 coated raised island structures 322 that are attached to a flexible backing sheet 330 where abrasive agglomerate beads 318, 326 containing abrasive particles 332 are supported by the adhesive 320. The adhesive layer 320 has an adhesive thickness 338. The diameter (or size) of the abrasive beads 328 is used as a reference for establishing the control, or allowable variation, of the height 334 of the island structure 322 as measured from the top of the non-adhesive coated island structure 322 to the backside of the abrasive article backing sheet 330. The diameter (or size) 328 of the abrasive beads 318, 326 is also used as a reference for establishing the control, or allowable variation, of the height (or thickness) 336 of the raised island abrasive article 324 as measured from the top of the island beads 326 to the backside of the abrasive article backing sheet 330. The heights (or thicknesses) 336, 334 are controlled to have a standard deviation, or size variation, that is only a percentage of the size 328 of the abrasive beads 318, 326 where the standard deviation is typically less than 50% of the size 328 of the abrasive beads 318, 326. Having island structures 322 that have a precision heights 334 aids in the manufacturing of abrasive articles 324 that have precision thicknesses 336. However, it is the precise height 336 or thickness 336 of the abrasive article 324 that provides the desired performance of the precision flatness abrasive article 324. It is desired that the abrasive beads 318, 326 have a small diameter of a preferred size of 45 micrometers (0.002 inches) for abrasive lapping articles 324 as a bead size 318 that is smaller than this does not provide enough abrasive for a significant abrading life of an abrasive article and beads 318, 326 that are much larger than this provide too much variation in the thickness of the article 324 bead 318, 326 abrasive layer which results in uneven or non-flat article 324 abrading surfaces after some abrading usage of the article 324. Therefore, it is critical that the abrasive article 324 thickness 336 have a standard deviation of less than 50% of the desired 45 micrometers (0.002 inches) bead size 328 or a deviation of less than 23 micrometers (0.001 inches) and it is more preferred that the deviation be less than 10 micrometers (0.0004 inches) and even more preferred that the deviation be less than 5 micrometers (0.0002 inches). None of the disclosures in the referenced prior art patents address this issue of the control of the standard deviation of the overall thickness 336 of the abrasive article 324.
U.S. patent application No. 2003/0143938 (Braunschweig et al.) describes island-type abrasive articles having backings that have raised island structures that are top coated with shaped-abrasive coatings while the article backside has a mechanical engagement system.
U.S. patent application No. 2003/0207659 (Annen et al.) describes island-type abrasive articles having backings that have raised island structures that are top coated with shaped-abrasive coatings. The backings include polymer foam backings. Raised island structures are attached on backing sheets by a variety of methods including the use of belts and rolls having island shaped cavities that are filled with a polymer or foam structure material that is deposited onto and attached to the backing sheet. A mixture of abrasive particles and polymer resins are then formed into geometric shapes, preferably pyramid shapes, onto the raised island top surfaces. The pyramids are formed by coating the abrasive slurry on a shape-patterned tooling belt or a shape-patterned rotogravure roll and bringing a backing into contact with the roll or belt to transfer the shaped-abrasive coating onto the raised island surfaces. It is desirable that the tooling belt be made of a polymer material, using a master belt to produce the polymer tooling belts. These abrasive pyramids are similar to the shaped abrasive pyramids sold by 3m Company under the trade designation “TRIZACT™ as abrasive sheet lapping articles. There is no teaching of the importance of controlling the height of the raised island structures or of controlling the exact thickness of the shaped abrasive island coatings that would allow this product to be used effectively in high speed or precision flat lapping. In fact, reference is made specifically that island structures may have varying heights. One intended use of this abrasive-island product is to reduce “stiction”, a form of friction, between the abrasive article and the workpiece. Stiction is defined by Annen as the condition whereby the combination of a coolant fluid and a smooth abrasive coating creates a condition whereby the fluid acts as a adhesive between the abrasive coating and the workpiece surface which causes these surfaces to stick together with unwanted results. Stiction tends to occur frequently with lapping type abrasive articles where the abrasive particles are imbedded in a binder which provides a smooth surface to these abrasive sheet articles. The shaped abrasive coatings are a mixture of abrasive particles mixed with a polymer binder that is applied to the flat top surfaces of the raised island structures in a pattern of shaped abrasive bodies. Each shaped body is formed into a geometric shape, including pyramid shapes, where each formed shaped body has a individual height and a volume and body base area and where each shape body has raised and recessed portions. The presence of the recessed valley areas between the raised island structures allows fluid flow at the working face of the abrasive article without undesirable stiction taking place. It is suitable for casual polishing rather than for controlling both the flatness and smoothness of the surface rather than precision flat lapping of workpieces. Triangular shaped abrasive coatings in general do not provide the even wear across the surface of a workpiece that is required for flat lapping due to the geometric shape of abrasive island coating. The tips of the abrasive triangles volumetrically contain very little abrasive material and are very fragile while the triangle base areas contain the bulk of the abrasive material. During abrading action, the tips wear down very rapidly which changes the overall flatness of the abrasive article dramatically in those surface areas where a workpiece first contacts the abrasive article. When a new workpiece is then positioned at an article surface area that has sub-section areas of worn-down-tips and adjacent un-worn shaped abrasive tips, the workpiece surface is abraded unevenly by both the tip-worn and tip-non-worn shaped abrasive areas. The preferred construction materials, including non-precision foam backings and foam island structures, and sequential manufacturing techniques, including the use of master belts to produce replicated polymer belts that are used to form shaped abrasive coatings, and the use of thick and fragile shaped abrasive coatings that are not thickness-controlled as described here by Annen, taken together, prevent the production of precision height or overall-thickness controlled abrasive articles. In comparison, precision abrasive articles that can successfully produce both flat and smooth workpiece surfaces require durable and equal-sized abrasive beads or coatings that are bonded onto stable and strong island structures that are precision height controlled relative to the backside of the abrasive article backing sheet. None of these critical abrasive article design feature issues are addressed by Annen.
FIG. 25 (Prior Art) is a cross section view of the Annen raised islands attached to a backing sheet where the islands have pyramid shaped abrasive coatings. The island structures 272 are attached to a backing sheet 266 and the flat top surfaces of the island structures 272 are covered with pyramid shaped bodies 270 that contain abrasive particles 268 which are mixed in a polymer binder 271. The shaped pyramid bodies 270 have a height 274 as measured from the top flat surface of the island structures 272 to the apex of the pyramid body 270. The raised island structures 272 have a height 276 measured from the top of the island structure 272 to the backside of the backing 266. The overall thickness 269 of the abrasive article 267 is measured from the top of the abrasive shaped pyramids 270 to the backside of the backing 266. Control of the variance of the height 274 of the pyramids 270 or variance in the overall abrasive article 267 thickness 269 is not discussed by Annen, which indicates a lack of awareness of the article size control features that are required for an abrasive article such as this to be successfully used for precision flatness high speed lapping. When the abrasive pyramids that are attached to the island surfaces of an abrasive article that has raised island structures, or the pyramids are attached to the flat surface of an abrasive article that does not have raised island structures, there tends to be large dimensional wear-down changes in the thickness of the abrasive article even though little of the volume of the abrasive material is worn away. FIG. 25A, FIG. 25B, FIG. 25C and FIG. 25D (all Prior Art) are cross section views of the Annen pyramid shaped abrasive bodies that are shown in FIG. 25 as the abrasive pyramids are bonded to the top surfaces of raised island structures which are attached to a backing sheet. The abrasive pyramids are shown in the original as-formed, full-height pyramids and then in progressive stages of wear-down, which has a large effect on the height of the pyramids even though little of the volume of abrasive material has been expended in the abrading wear process. FIG. 25A (Prior Art) is a cross section view of an Annen original as-formed pyramid shaped abrasive body where the abrasive pyramid body 280 is attached to a backing sheet 282 and the pyramid 280 has a full height 281 that is measured from the apex of the pyramid 280 to the base of the pyramid 280. FIG. 25B (Prior Art) is a cross section view of an Annen abrasive pyramid shaped abrasive body where the abrasive pyramid body 284 has 25% of the original pyramid 280 height, as shown in FIG. 25A, worn away. The pyramid 284 is attached to a backing sheet 282 and the pyramid 284 has a new height 285 that is measured from the worn upper flat surface of the pyramid 284 to the base of the pyramid 284. The abrasive pyramid has been reduced in height by 25% but the volumetric loss of abrasive material from the original square pyramid volume is only 1.5% of the original volume. FIG. 25C (Prior Art) is a cross section view of an Annen abrasive pyramid shaped abrasive body where the abrasive pyramid body 286 has 50% of the original pyramid 280 height, as shown in FIG. 25A, worn away. The pyramid 286 is attached to a backing sheet 282 and the pyramid 286 has a new height 288 that is measured from the worn upper flat surface of the pyramid 286 to the base of the pyramid 286. The abrasive pyramid has been reduced in height by 50% but the volumetric loss of abrasive material from the original pyramid volume is still only 12.5% of the original volume. FIG. 25D (Prior Art) is a cross section view of an Annen abrasive pyramid shaped abrasive body where the abrasive pyramid body 290 has 75% of the original pyramid 280, as shown in FIG. 25A, worn away. The pyramid 290 is attached to a backing sheet 282 and the pyramid 290 has a new height 292 that is measured from the worn upper flat surface of the pyramid 290 to the base of the pyramid 290. The abrasive pyramid has been reduced in height by 75% but the volumetric loss of abrasive material from the original pyramid volume is still only 42% of the original volume which means that 58% of the abrasive material contained in the original pyramid still remains in the worn-down pyramid body. When the abrasive article is worn down this much, it is typical that some areas of the abrasive article will wear down much more rapidly than other areas due in part to the location of the workpiece on a specific area of a abrasive article. Also, high spots that initially existed on a workpiece surface will wear down localized portions of the abrasive article surface more than other portions. These worn-down abrasive areas then will not effectively contact a flat workpiece surface during subsequent abrading action. This is a significant reason to limit the initial thickness of an abrasive layer coated on an abrasive article specifically to limit the out-of-plane wear down of a portions of the abrasive article during repetitive abrading use. When an abrasive article is worn into a non-flat condition, it now becomes difficult to generate a flat abrasive surface on a workpiece in precision flat lapping. Non-flat abrasive article areas can produce non-flat workpiece surface areas, which is objectionable. Use of arrays of pyramid shapes of an abrasive particle binder mixture that is coated on the top flat surfaces of raised island structures increases the non-flat wear-down of abrasive articles because so little abrasive material exists at the apex areas of the individual pyramids which results in fast wear-down of the pyramid apex or tip areas. Annen states the desirability of the abrasive article providing a constant abrasive cut rate but this constant cut rate is very difficult to provide with the pyramid shaped abrasive shaped forms. The cut rate, or material removal rate, of an abrasive is related to the contact pressure (force per unit area) that is applied to the abrasive material that is in contact with a workpiece surface. When a pyramid shaped abrasive structure is worn down, the abrading contact area of the pyramid changes rapidly from a very small area to a very large area. In their original full-sized shape, the pyramid top surfaces have very little area in contact with a workpiece as the applied abrading contact force is concentrated into the small contact areas at the apex of the individual pyramids. As the abrading pressure is equal to the abrading force divided by the abrading area, a very large pressure and very large material removal rate is present when a pyramid shaped abrasive is first used. The sharp apex contact areas of a new pyramid abrasive article even has the capability of scratching a workpiece rather than polishing it due to these concentrated abrasive contact areas. As the pyramids are worn down, a process that occurs rapidly during the first stages of abrading use, the contact area of the individual pyramids also collectively increases very rapidly. Adjusting the abrading contact force to accurately compensate for the change of abrasive contact area to achieve the same or a constant cut rate is difficult to accomplish. As an example, the top surface area of a triangular shaped pyramid has an extremely small surface area so the contact pressure, consisting of the applied contact force divided by the contact area, is very high. This pressure results in high and localized workpiece cut rates that exists only at the location of the pyramid tips. Workpiece surface areas that are located adjacent to the pyramid tips get no abrading action at all as these adjacent areas are not in contact with the workpiece surface. The change of the pyramid top surface contact areas of worn-down pyramids is very large. A sharp-topped pyramid initially has an infinitesimally small contact area, depending on how sharp the apex of the pyramid is before wear occurs. When 25% of the original pyramid is worn down the pyramid has a flat top and has a truncated pyramid shape that has a small but significant top area that is considered here, for comparison, to have a unity (1.0) sized area. When 50% of the original pyramid is worn away, the pyramid top surface area is now 4.0 times greater than the unity 1.0 area of the 25% worn pyramid. When 75% of the original pyramid is worn away, the pyramid top surface area is now 9.0 times greater than the unity 1.0 area of the 25% worn pyramid. There is still 58% of the original abrasive left in the pyramid at this stage of wear. The pyramid will continue to wear down, the abrading contact surface area will continue its large non-proportional increase and the abrading contact pressure will continue the rapid change reduction. This huge abrading contact area change will produce non-constant wear over the abrading life of the abrasive article having the pyramid shaped abrasive structures coated on the top surfaces of the raised islands. However, this well-worn abrasive article can still provide smooth polishing of a workpiece surface even though the workpiece material removal rate may not be accurately controlled. Also, the large dimensional change in the thickness of portions of an abrasive article having pyramid abrasive shapes on its surface can tend to prevent the workpiece surface being abraded into a precisely flat surface. This series of pyramid wear-down FIGS. 25A-25D also demonstrate why it is impractical to use expensive diamond particle abrasives in the pyramid formed bodies as so much of the abrasive resides in the lower elevations of each pyramid where they will not be used effectively in precision flat lapping in either low speed or high speed operations.
In general, the features described by Annen are of non-precision height or thickness controlled abrasive articles that are produced by mass production continuous web processes that each add an element of size, thickness or other dimensional location variability to the finished article. The location of the individual formed polymer resin pyramid, and other, shapes on the top surfaces of the individual raised island structures is not discussed. Many of the web or sheet or belt or roll shape forming techniques he uses will tend to position some of the individual shaped abrasive shapes on, or over, the edges of the top surfaces of the island structures which will leave them in a precarious structural location. Each of these individual abrasive shapes needs to be firmly anchored to the structure top surface to provide sufficient structural strength to resist the very high local abrading forces that are applied to these individual shapes as they are providing abrading action to the workpiece surface. These localized abrading forces can become significantly high when an individual formed abrasive shape contacts a physical deformity or material inclusion that exists at or on the surface of a workpiece. If the individual abrasive shape is not sufficiently anchored to the raised island structure, either part of or the whole abrasive formed shape can be knocked off the abrasive article and cause a scratch to occur on the workpiece surface during this event. This is very undesirable for workpiece lapping. Because of this shape bond strength vulnerability, the formed abrasive shapes should not overhang the edges of the raised island structures. Also, the surfaces of each raised island should in general be flat, and in particular, the edge areas of the island structures in the areas that support each individual abrasive shape should be flat to provide a structural support to the abrasive shapes. The manufacturing techniques described to form the abrasive shapes generally provide an array of like-sized abrasive shapes that lie in a plane and there is no capability to position an individual abrasive shape on a non-flat island structure. This same problem can occur on the non-flat inner area portion of raised islands rather than just the non-flat island edge portions. An individual abrasive pyramid shape will not be properly attached to a non-flat island surface. FIG. 25 (Prior Art) shows abrasive pyramid bodies 270 that are intentionally shown overhung a distance 265 from the raised island structure 272. Also shown is a border gap that has a gap distance 263 that is a measure of the distance that the abrasive pyramid body 272 could be positioned from the edge of the raised island structure 272 to assure structural attachment stability of the abrasive body 272 as it is attached to the island structure 272. The pyramid body overhang distance 265 and gap 263 as shown here, are not disclosed by Annen.